The Soma cube is a three-dimensional version of the 12 pentomino problem in which a 6 x 10 grid has to be covered, the later is a classic Canterbury puzzle. Around 1982 I once wrote a Pascal computer program (with turtle graphics) which computed by recursive backtracking all solutions and even animated them on an apple school computer and remember having been asked to leave the lab because a supervisor thought I play games. I learned about the combinatorial search problem to find the number of solutions from Ralph Ehrismann who had like me participated in the Schweizer Jugend Forscht project and had written there a program to compute the 2339 solutions.

I had in high school also been fascinated by the problem to find the number of n-polyominos and tried hard to find a law. I learned only later that the problem is hard as it is a self-avoiding random walk problem. They are also called lattice animals. It is a difficult combinatorial problem with applications in statistical mechanics. There are 12 pentominos. (Tetris bricks). The 35 hexominos can not be used to tile a rectangle however. Then there are 108 heptominoes. The 107 simply connected heptominoes can tile a 7 * 107 rectangle. Then there are 369 octominoes and 1285 nonominoes and and 4655 decominos.

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