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 A382309 #14 Apr 02 2025 07:04:46 %S A382309 1,1,5,147,7819,655315,81255642,13985577438,3191399514435, %T A382309 932692830330915,339781108888268398,150979116192562395562, %U A382309 80377829037419610855326,50509994170589416909171726,36995186973806250851237265812,31240798437883511927927569474140 %N A382309 Number of permutations of [2n] with exactly n ascents and an even number of inversions. %H A382309 Alois P. Heinz, <a href="/A382309/b382309.txt">Table of n, a(n) for n = 0..225</a> %H A382309 Wikipedia, <a href="https://en.wikipedia.org/wiki/Inversion_(discrete_mathematics)">Inversion</a> %H A382309 Wikipedia, <a href="https://en.wikipedia.org/wiki/Permutation">Permutation</a> %F A382309 a(n) = A128612(2n,n). %F A382309 a(n) ~ sqrt(3) * 2^(2*n) * n^(2*n) / exp(2*n). - _Vaclav Kotesovec_, Apr 02 2025 %Y A382309 Cf. A128612, A180056. %K A382309 nonn %O A382309 0,3 %A A382309 _Alois P. Heinz_, Mar 21 2025