Coprime picking game on the integers 2 to 30
Question
Two players, Alice and Bob, alternately pick integers from . Whoever first picks a number having a common factor greater than with some number already chosen loses. Alice may decide whether she moves first or second, and both play perfectly. Put if Alice should move first and if she should move second. It turns out Alice has exactly six winning opening picks . Compute .
Short answer
115. Alice should start (). Picking (or ) kills primes and ; after that every remaining safe number uses exactly one of the primes , so moves just knock out one prime each and Bob runs out first. Opening with or also wins (confirmed by exhaustive search), giving .
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