This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A177286 #9 May 30 2025 23:51:42 %S A177286 1,1,6,90,2520,113400,7484400,349272000,12629539440,394462558980, %T A177286 11673071453460,348672825749478,10924880404749722,348078897908489130, %U A177286 11059657083803795688,346844915294462956440,10705742604901078977600 %N A177286 Number of permutations of 2 copies of 1..n with all adjacent differences <= 5 in absolute value. %C A177286 a(n) = (2n)!/2^n for n<=6. %Y A177286 Cf. A177282, A177283, A177284, A177285, A177287, A177288, A177289, A177290, A177295. %K A177286 nonn %O A177286 0,3 %A A177286 _R. H. Hardin_, May 06 2010 %E A177286 a(0)=1 and a(12)-a(16) from _Max Alekseyev_, May 30 2025