Jigsaw Numbers

Jigsaw puzzles come in very different shapes and sizes, but there are some constraints.

We will call a number N N a jigsaw number if it is the number of pieces of a jigsaw puzzle whose length is less than twice its width. For instance, 48 is a jigsaw number because 48 = 8 × 6 48 = 8\times 6 and 8 < 2 6 8 < 2\cdot 6 ; but 32 is not a jigsaw number because its decompositions 32 × 1 32\times1 , 16 × 2 16\times2 , or 8 × 4 8\times4 do not have a length less than twice its width.

How many jigsaw numbers N N are there such that 1000 < N < 10000 1000 < N < 10000 ?


The answer is 2562.

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1 solution

Giorgos K.
Feb 23, 2018

Mathematica

Length@Select[Range[1001,9999],#[[2]]<2#[[1]]&@Quantile[Divisors@#,{.5,.51}]&]

2562

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