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 A321629 #4 Dec 09 2018 12:32:40 %S A321629 1,1,1,2,3,1,4,8,5,1,10,22,18,7,1,26,62,60,32,9,1,76,184,194,126,50, %T A321629 11,1,232,568,630,462,228,72,13,1,764,1840,2072,1644,938,374,98,15,1, %U A321629 2620,6204,6972,5788,3650,1710,572,128,17,1 %N A321629 The Riordan square of the permutation involutions. Triangle T(n, k), 0 <= k <= n, read by rows. %C A321629 The Riordan square is defined in A321620. %e A321629 [0] 1; %e A321629 [1] 1, 1; %e A321629 [2] 2, 3, 1; %e A321629 [3] 4, 8, 5, 1; %e A321629 [4] 10, 22, 18, 7, 1; %e A321629 [5] 26, 62, 60, 32, 9, 1; %e A321629 [6] 76, 184, 194, 126, 50, 11, 1; %e A321629 [7] 232, 568, 630, 462, 228, 72, 13, 1; %e A321629 [8] 764, 1840, 2072, 1644, 938, 374, 98, 15, 1; %e A321629 [9] 2620, 6204, 6972, 5788, 3650, 1710, 572, 128, 17, 1; %p A321629 # The function RiordanSquare is defined in A321620. %p A321629 cf := proc(dim) local k, m; m := 1; %p A321629 for k from dim by -1 to 1 do m := 1 - k*x - k*x^2/m od; %p A321629 1/m end: RiordanSquare(cf(9), 9); %Y A321629 First column are the self-inverse permutations A000085. %Y A321629 Row sums are A193777, alternating row sums are A000007. %Y A321629 Cf. A321620. %K A321629 nonn,tabl %O A321629 0,4 %A A321629 _Peter Luschny_, Dec 09 2018