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 A383835 #20 May 19 2025 17:58:14 %S A383835 1,1,2,4,12,28,76,232,776,2632,9496,35696,140272,568624,2390480, %T A383835 10349536,46208416,211800992,997313824,4809701440,23758694336, %U A383835 119952723136,618884638912,3257843882624,17492191242880,95680444425856,532985208200576,3020676745975552 %N A383835 Number of permutations of [n] whose compositional square is the identity permutation or its reverse. %F A383835 a(n) = A000085(n) + A037224(n) for n > 1. %e A383835 a(4) = A000085(4) + A037224(4) = 10 + 2 = 12: 1234, 1243, 1324, 1432, 2134, 2143, 3214, 3412, 4231, 4321, 2413, 3142. %Y A383835 Cf. A000085, A000142, A037224. %K A383835 nonn,easy %O A383835 0,3 %A A383835 _Darío Clavijo_, May 11 2025