# 2937: Room Code

## Explanation[edit]

Cueball and Megan are on vacation or otherwise traveling, and receive a code for their hotel room. Megan gives a seemingly nonsensical and unhelpful mnemonic by which Cueball can remember it... which, inexplicably, actually *helps* Cueball to remember the code. Cueball becomes VERY angry on realizing this.

The first three prime numbers are actually 2, 3, and 5. So this technique easily identifies the first two digits "02". "05" is slightly wrong because it's not the second prime number; it's the third. And "18" is even more wrong because it's not actually a prime number; it's 2 × 3 × 3.

So the mnemonic itself doesn't really provide the method for remembering the code. Instead, figuring out how to apply the bogus mnemonic will reinforce your memory of the code. Unless you actually happen to be really bad at prime numbers and panicked while remembering them, in which case the bad mnemonic actually... helps?! Why is your memory like this?!

The title text points out that the code is also similar to a date in the (potentially ambiguous) MMDDYY format - not an unexpected choice, seeing as Randall lives in the United States - so if you happen to have a relative who was born on February 5th 2018, the memorized code will help you remember this date if using said date format. It is also a valid date in the DDMMYY format but in that case it would be the 2nd of May 2018, or in YYMMDD format, in which case it refers to 18th of May 2002.

## Transcript[edit]

- [Megan is standing next to Cueball, who is holding a phone or a note in his hand. Each one has a suitcase on the out-facing side of them.]
- Cueball: Okay, I need to remember that the room code is 020518.

- [Closeup on Megan who has her palm raised.]
- Megan: Easy -- just memorize it as "the first three prime numbers, if you realized you couldn't remember what came after 2 and started to panic and get them increasingly wrong."

- [Beat panel of Megan and Cueball standing with no border.]

- [Megan and Cueball still standing.]
- Megan: ...Are you mad because that actually works?
- Cueball:
**Why is memory like this?**

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# Discussion

Obviously, for many of us it would be more helpful as a mnemonic for a slightly older relative born on May 18, 2002. But since the author is American, it is of course reasonable for him not to have mentioned this. 162.158.134.235 20:36, 24 May 2024 (UTC)

- ISO-8601 FTW.
- ProphetZarquon (talk) 14:05, 25 May 2024 (UTC)
- Do "many" of you use YYMMDD though? YY rather than YYYY? Many, many of us use DDMMYY though. Yorkshire Pudding (talk) 20:46, 24 May 2024 (UTC)
- UK resident here. I have only used YYYYMMDD at the start of file names to manually produce versioning order.RIIW - Ponder it (talk) 07:30, 25 May 2024 (UTC)
- Another Brit. Having dealt with transatlantic stuff, I switched to YYYY/MM/DD exclusively due to being utterly fed up with trying to work out when an ambiguous date (like in this example, or the infamous 9th of November) was supposed to be. 172.71.131.158 21:40, 26 May 2024 (UTC)
- This particular Brit (also veteran of Y2K, at the same time as regularly "talkin' to 'Merkins" and having to make sure I don't confuzzle them either with what a Rightpondian would write or by them
*assuming*that I'm writing in Rightpondian when I'm not) continues to tend to use DD/Mmm/YYYY for anything with a human-reading focus. Or something like YYYYMMDD(-hh(mm(ss))), as per RIIW's situational reasoning where dumb alphanumeric ordering might dominate in primarily computer-reading scenarios. 172.69.79.164 23:32, 26 May 2024 (UTC)- I know that people in the Netherlands use YYMMDD for dates - I used to work for Philips research (a Dutch company) - and they used that format everywhere. It's actually VERY logical because if you write a decimal number 12,345 you put the most significant digit first...so YYMMDD does the same thing - the year being the more significant. One GREAT thing about that representation is that a simple numerical sort will get things into date-wise ordering. I've heard that some countries write addresses that way too: USA / Texas / Dallas / MainStreet / 123...again, putting the most significant information first. 162.158.140.153 14:39, 30 May 2024 (UTC)

- This particular Brit (also veteran of Y2K, at the same time as regularly "talkin' to 'Merkins" and having to make sure I don't confuzzle them either with what a Rightpondian would write or by them

- Another Brit. Having dealt with transatlantic stuff, I switched to YYYY/MM/DD exclusively due to being utterly fed up with trying to work out when an ambiguous date (like in this example, or the infamous 9th of November) was supposed to be. 172.71.131.158 21:40, 26 May 2024 (UTC)

- UK resident here. I have only used YYYYMMDD at the start of file names to manually produce versioning order.RIIW - Ponder it (talk) 07:30, 25 May 2024 (UTC)
- Yes, add me to the "2nd of May" club. (Or whatever young relative I can retrospectively induce to join, anyway.) 172.69.79.165 22:58, 24 May 2024 (UTC)
- Yes, of course DDMMYY is a thing as well (although I would have expected dots or something), I might have mentioned that. Here in Sweden, YYMMDD is very common, along with YYYY-MM-DD, D/M YYYY and YYYYMMDD (the latter increasingly so, very rare before y2k). YY-MM-DD and D/M -YY are rather less common (after y2k). Formats with dots or Roman numerals are almost unheard of, as are middle-endianness and anything with slashes before or after the year. Source: subjective experience.) (Of course, many Swedes also realize that months have names that alleviate ambiguity.) 162.158.134.242 04:30, 25 May 2024 (UTC)
- Now I want some kind of joke about Your Mileage May Vary, but it's some variation of YYDMDM. (Yes Your Date May Deviate Massively?)
- ProphetZarquon (talk) 14:12, 25 May 2024 (UTC)

- My birthday is actually May 18, XXXX, and I am American, but I always use XX0518 for a 6 number code.

- Which brings up 2562:_Formatting_Meeting (I ~~don't know~~ figured out how to do internal links) 172.71.22.80 20:52, 24 May 2024 (UTC)
- I know that State Side, they say that as you write May 2nd 2024, then it's right to have MMDDYYYY, but they celebrate the 4th of July! However, in the UK we are likely to date letters 2nd May, 2024. RIIW - Ponder it (talk) 07:30, 25 May 2024 (UTC)
- Now I want some kind of joke about Your Mileage May Vary, but it's some variation of YYDMDM. (Yes Your Date May Deviate Massively?)
- ProphetZarquon (talk) 14:12, 25 May 2024 (UTC)
- YMMD (Your Mileage May Differ) 162.158.129.253 (talk) 08:52, 27 May 2024
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- YMMD (Your Mileage May Differ) 162.158.129.253 (talk) 08:52, 27 May 2024

- I know that State Side, they say that as you write May 2nd 2024, then it's right to have MMDDYYYY, but they celebrate the 4th of July! However, in the UK we are likely to date letters 2nd May, 2024. RIIW - Ponder it (talk) 07:30, 25 May 2024 (UTC)
*"I don't know how to do internal links"*At the very bottom of the Editing page, "**Editing help (opens in new window)**", which goes to https://www.mediawiki.org/wiki/Help:Links and you want "**Internal links**" --PRR (talk) 00:11, 25 May 2024 (UTC)- In case it helps, I've just written something, at least so long as that user doesn't delete or change my contribution which summarises (badly?) the general gamut of linking options you might need to employ here. It's tuned to explainxkcd usage, rather than the full (in their own way) and perhaps more precise wikipedia standards that the above link gives. And it was written on the spur of the moment, not really so carefully edited. But FYI. 162.158.38.70 21:04, 25 May 2024 (UTC)

- Also related 1179:_ISO_8601 --172.71.160.93 09:09, 27 May 2024 (UTC)

- Do "many" of you use YYMMDD though? YY rather than YYYY? Many, many of us use DDMMYY though. Yorkshire Pudding (talk) 20:46, 24 May 2024 (UTC)
- Can totally relate as a 020506. Whichever of the six ways it may be read ig… 172.70.90.65 10:09, 22 June 2024 (UTC)

wait...so y'all actually don't need help with remembering numbers? oh. I can usually memorize like 10 long strings of random numbers almost instantly by finding patterns through them. order through chaos? 42.book.addict (talk) 02:13, 25 May 2024 (UTC)

- These patterns are a kind of mnemonic, duh. Only works if you're comfortable enough with numbers (to be able to find some pattern in any digit string), otherwise one should use a more familiar association. 172.68.194.201 14:58, 25 May 2024 (UTC)

I usually remember numbers with their pattern on computer or telephone keys. When I recite π, I start moving my hand through the air at some point. Here the even position digits are ascending in the middle and the others are 001, so quite easy. Fabian42 (talk) 03:39, 25 May 2024 (UTC)

- I remember random information by putting it in my phone! RIIW - Ponder it (talk) 07:30, 25 May 2024 (UTC)

He forgot to dot the question mark. 🤭 --162.158.74.68 09:41, 25 May 2024 (UTC)

I always have a pen to write on my hand for this reason tbh Psychoticpotato (talk) 03:31, 26 May 2024 (UTC)

- The trouble is, most people couldn't do it for this doorcode. It has six digits, but the typical hand only ever has five! 172.69.194.207 09:03, 26 May 2024 (UTC)
- Hello. My name is Inigo Montoya. 172.68.194.178 09:50, 26 May 2024 (UTC)
- .207, you made me laugh. Good job. (genuinely) Psychoticpotato (talk) 21:09, 5 June 2024 (UTC)
- The average hand has less than 5 digits. SDSpivey (talk) 01:28, 28 May 2024 (UTC)
- Average =/= Typical (unless it's a modal average).172.70.90.177 08:13, 28 May 2024 (UTC)
- Hey, there's a comic about this. 2696: Precision vs Accuracy -Psychoticpotato (talk) 21:20, 11 June 2024 (UTC)

- Average =/= Typical (unless it's a modal average).172.70.90.177 08:13, 28 May 2024 (UTC)

The room code 020518 as listed consists of prime numbers 2 and 5 (with 3 missing). however both are preceded by a zero. The 18 is interpreted as non prime (it is not) but the 2x3x3 seems a bit far off from any prime. Would the alternative explanation 0-5 is a zero followed by the prime number five --- followed by 1 - 8 which is 0+1 and 7+1 which could be logical continuation of 0+0-5+0, 0+1-7+1, followed by e.g. 0+2, 11+2 etc. - as such series sometime go. 172.70.46.193 14:10, 26 May 2024 (UTC)

- Support for this idea: 02, skip three for 05, the next prime is 07, but you are "increase"-ingly wrong, so you increase both digits to get 18.
- It may be "far off" from being prime in a factorization sense, but it's quite close to being a prime because it's right next to both 17 and 19, which are both prime. Admiral Memo (talk) 11:56, 29 May 2024 (UTC)
- What would be interesting would be to find 'twinned Mersennes', i.e. specifically that (2^n)-1
*and*(2^n)+1 are both prime. (Currently, I can only identify n=2 as valid for that, but I'm not immediately aware of any reason why (2^n)+1 might not be equally valid as (possible) prime, nor why it might only pair with a non-prime (2^n)-1 'mersenne miss' number.) By the above logic, (2^n) iteself would quite close to being a prime (being another prime-pair's intermediate) whilst being quite conspicuously factorisable to the*n*th order. 172.71.178.131 13:57, 29 May 2024 (UTC)

- What would be interesting would be to find 'twinned Mersennes', i.e. specifically that (2^n)-1

I remember my 628496 was my room code for a while back at uni, very easy to remember as the first three Perfect Numbers 172.70.163.121 (talk) 08:25, 28 May 2024 *(please sign your comments with ~~~~)*

It's three prime numbers if you assume two digits per number and base 9. Translating that to base 10 would be: 2, 5, 17 -- Cwallenpoole (talk) 18:50, 12 June 2024 *(please sign your comments with ~~~~)*

So, what about this explanation still needs work? What's incomplete, unclear, or questionably accurate? GreatWyrmGold (talk) 04:21, 25 June 2024 (UTC)