The current puzzle is… puzzling: Given the set {1,…,N} with N<61, one iterates the following procedure: take (x,y) within the set and replace the pair with the smallest divider of x+y (bar 1). What are the values of N such that the final value in the set is 61? I find it puzzling because the […]
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Le Monde puzzle [#820]
May 15, 2013Le Monde puzzle [#818]
May 1, 2013The current puzzle is as follows: Define the symmetric of an integer as the integer obtained by inverting the order of its digits, eg 4321 is the symmetric of 1234. What are the numbers for which the square is equal to the symmetric of the square of the symmetric? I first consulted stackexchange to find […]
Le Monde puzzle [#817]
April 19, 2013The weekly Le Monde puzzle is (again) a permutation problem that can be rephrased as follows: Find where denotes the set of permutations on {0,…,10} and is defined modulo 11 [to turn {0,...,10} into a torus]. Same question for and for This is rather straightforward to code if one adopts a brute-force approach:: (where I […]
Le Monde puzzle [#815]
April 12, 2013The last puzzle was as follows: Take a card stack with 32 cards and divide it into five non-empty piles. A move consists in doubling a pile size by taking card from a single and larger pile. Is it possible to recover the original stack by repeatedly using moves? Same question for 100 cards and five […]
Le Monde puzzle [#814]
April 2, 2013The #814 Le Monde math puzzle was to find 100 digits (between 1 and 10) such that their sum is equal to their product. Given the ten possible values of those digits, this is equivalent to finding integers a1,…,a10 such that a1+…+a10=100 and a1+2a2+…+10a10=2a2x….x10a10, which reduces the number of unknowns from 100 to 10 (or […]
