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 A177290 #8 Jan 05 2022 06:43:56 %S A177290 1,1,6,90,2520,113400,7484400,681080400,81729648000,12504636144000, %T A177290 2375880867360000,367786358267328000,47683626117839712000 %N A177290 Number of permutations of 2 copies of 1..n with all adjacent differences <= 9 in absolute value. %F A177290 a(n) = (2n)!/2^n for n<=10. %Y A177290 Cf. A000680. %K A177290 nonn,more %O A177290 0,3 %A A177290 _R. H. Hardin_, May 06 2010 %E A177290 a(0)=1 prepended and a(12) added by _Alois P. Heinz_, Jan 05 2022