# 247: Factoring the Time

Factoring the Time |

Title text: I occasionally do this with mile markers on the highway. |

## Explanation

Cueball is bored, so he has been calculating the prime factors of the time shown on the clock. The prime factor of a positive number is a number which could be divided only by prime numbers. Cuball is been doing this for almost two hours (from 1:00 pm to 2:53 pm). The number 2 is the smallest prime but is not a factor of 253, which is an odd number. The smallest prime factor of 253 is 11, which makes the other factor 23.

His co-worker decides to mess with Cueball and so he switches the clock from 12-hour time (2:53 pm) to 24-hour time (14:53). This makes factorization more difficult, as the time now shown is a four digit number rather than a three digit number. The number 1,453 is actually a prime number and so has no factors but one and itself. Cueball has exactly one minute to determine this, which is nearly impossible to be done by a human brain..

In the title text, Randall claims he applies the same challenge to highway location markers. At highway speeds (60+ mph), they would show up at least once per minute. Combined with the need to also concentrate on driving, factorizing numbers in the allowed time becomes much more difficult despite the lower numbers on the markers.

## Transcript

- [One man is sitting at a computer. Cueball sits at a separate desk. There is a clock which reads 2:53.]
- Cueball: 253 is 11x23
- Man at computer: What?
- Cueball: I'm factoring the time.
- Cueball: I have nothing to do, so I'm trying to calculate the prime factors of the time each minute before it changes.
- Cueball: It was easy when I started at 1:00, but with each hour the number gets bigger
- Cueball: I wonder how long I can keep up.
- [Man at desk reaches back and touches the clock.]
*BEEP*- [Clock now reads 14:53.]
- Cueball: Hey!
- Man at computer: Think fast.

## Trivia

- There is a widget for OS X to display the current time and its prime factors.

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# Discussion

I used to find the prime factors of the remaining distance until the next turn. It starts off difficult (for me) at 99 miles, etc. When it gets down to 30 miles, it gets easier. Then, at 9.9 miles, I have a tenth the time to factor 99 again, and it gets easier as the numbers get smaller. This is actually a pretty good way to pass the time while driving. 108.162.219.202 (talk) *(please sign your comments with ~~~~)*