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 A177289 #10 May 30 2025 23:16:44 %S A177289 1,1,6,90,2520,113400,7484400,681080400,81729648000,12504636144000, %T A177289 1522786801536000,152883132197796000,13219614969625864800 %N A177289 Number of permutations of 2 copies of 1..n with all adjacent differences <= 8 in absolute value. %F A177289 a(n) = (2n)!/2^n for n<=9. %Y A177289 Cf. A000680. %K A177289 nonn,more %O A177289 0,3 %A A177289 _R. H. Hardin_, May 06 2010 %E A177289 a(0), a(12) from _Alois P. Heinz_, May 30 2025