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 A177288 #11 May 30 2025 23:16:49 %S A177288 1,1,6,90,2520,113400,7484400,681080400,81729648000,7580424852000, %T A177288 569159625434400,36636506215016400,2141931687266957040 %N A177288 Number of permutations of 2 copies of 1..n with all adjacent differences <= 7 in absolute value. %F A177288 a(n) = (2n)!/2^n for n<=8. %Y A177288 Cf. A000680. %K A177288 nonn,more %O A177288 0,3 %A A177288 _R. H. Hardin_, May 06 2010 %E A177288 a(0), a(12) from _Alois P. Heinz_, May 30 2025