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 A364819 #12 Oct 21 2023 11:34:34
%S A364819 0,0,2,6,24,80,312,1152,4616,18384,77280,328352,1451712,6527616,
%T A364819 30299504,143322000,696359232,3448656512,17483842176,90301959744,
%U A364819 476270369600,2557007766912,13991998520832,77867819879936,441003737739264,2537848321044480,14843836828748672
%N A364819 Number of permutations p of [n] such that max(|p(p(i)) - i|)=1.
%F A364819 a(n) = Sum_{k=1..floor(n/4)} (n-2*k)! * A000085(n-4*k) / (k! * (n-4*k)!).
%Y A364819 Column k=1 of A364817.
%Y A364819 Cf. A000085.
%K A364819 nonn
%O A364819 2,3
%A A364819 _Seiichi Manyama_, Oct 21 2023