Cross them off round and round and the last two standing are 16 and 31, with 16 going first.
Forty-one men stand in a circle, numbered 1 to 41. Counting round from number 1, every third man is killed, so 3 goes first, then 6, then 9, and the count carries on round the circle, skipping the gaps, until one man is left. Which number survives?
Give me a hintThe hint
There is no neat formula for every third man. Write the numbers out and cross them off.
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Number 31
Source: Claude Gaspard Bachet de Méziriac, after Flavius Josephus, 1612