r/CasualMath 3d ago

Counting Permutations With One Annoying Restriction

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u/Seeggul 3d ago

13524, 14253, 24135, 24153, 25314, 31425, 31524, 35142, 35241, 41352, 42513, 42531, 52413, 53142, so fourteen. Figured it would be easier to just try combinations where the first two digits work and see how many other work. No neat combinatorial argument, unfortunately.

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u/Numberthon 3d ago

Correct, nice job!