An arithmetics Le Monde mathematical puzzle: Find all bi-twin integers, namely positive integers such that adding 2 to any of their dividers returns a prime number. An easy puzzle, once the R libraries on prime number decomposition can be found!, since it is straightforward to check for solutions. Unfortunately, I could not install the recent […]

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## Le Monde puzzle [#913]

June 12, 2015## Le Monde puzzle [#910]

May 8, 2015An game-theoretic Le Monde mathematical puzzle: A two-person game consists in choosing an integer N and for each player to successively pick a number in {1,…,N} under the constraint that a player cannot pick a number next to a number this player has already picked. Is there a winning strategy for either player and for […]

## Le Monde puzzle [#909]

May 1, 2015Another of those “drop-a-digit” Le Monde mathematical puzzle: Find all integers n with 3 or 4 digits, no exterior zero digit, and a single interior zero digit, such that removing that zero digit produces a divider of x. As in puzzle #904, I made use of the digin R function: and simply checked all integers […]

## Le Monde puzzle [#905]

April 1, 2015A recursive programming Le Monde mathematical puzzle: Given n tokens with 10≤n≤25, Alice and Bob play the following game: the first player draws an integer1≤m≤6 at random. This player can then take 1≤r≤min(2m,n) tokens. The next player is then free to take 1≤s≤min(2r,n-r) tokens. The player taking the last tokens is the winner. There is […]

## Le Monde puzzle [#904.5]

March 25, 2015About this #904 arithmetics Le Monde mathematical puzzle: Find all plural integers, namely positive integers such that (a) none of their digits is zero and (b) removing their leftmost digit produces a dividing plural integer (with the convention that one digit integers are all plural). a slight modification in the R code allows for a […]