2. They begin reciting the positive natural numbers, in order, in a counter-clockwise direction (viewed from above), starting with the friend at the northern extreme of the circle (who utters "one").
3. As a friend utters an even number, he or she is eliminated from the counting (and consideration for lunch). The counting "wraps around" so that those who avoided one of the dreaded even numbers on the first round may be exposed on subsequent rounds.
4. The last person left is treated to lunch.
For example, if there are friends f1, f2, f3, f4, and f5 arranged counter-clockwise, with f1 at the northern extreme, the first round would eliminate f2 and f4. Then f1 and f5 would be eliminated in the next round, leaving f3 to enjoy the free lunch.
If there are n friends, where should you position yourself to get the free lunch? Do you have a technique that will work for any positive natural number n?
This is a problem on Professor Heap's Wiki and it was actually fun trying to come up with a solution :D
****So this is the pattern that I noticed:*****
There are specific numbers that correspond to a friend who is going to win
(ie.if n = 3, f3 wins)
and these numbers make a pattern where the next number to hold this similarity would be equal to
2(n) +1. This forms a geometric sequence {3,7,15,31...}. Then for the rest of the numbers, n, that don't fit in this sequence the friend who wins is equal to n, subtract the distance from the closest number in the geometric sequence (greater then n).
The Procedure for figuring out who wins:
1. Find the closest number in the geometric sequence {3,7,15,31...} of which have a difference of 2k + 1, where k is the previous number in the series.
2. Take a number, n, and subtract its distance from the closest number greater than it in the above series. That gives you the number of the friend who wins the pizza. If n is within the above sequence, then friend n wins.
Examples:
n = 5, f3 wins
n = 18, f5 wins
n = 15, f15 wins
So remember this game the next time you have only 1 pizza slice left and a bunch of hungry friends!!! Note. You can't have n < 3 because then you don't have a proper "circle".