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 A363232 #12 May 23 2023 08:16:06 %S A363232 1,1,1,1,7,3,1,37,66,19,1,175,975,990,219,1,781,12090,32575,23345, %T A363232 4231,1,3367,135903,866550,1514610,814903,130023 %N A363232 Triangular array read by rows. T(n,k) is the number of idempotent Boolean relation matrices with rank k, n >= 0, 0 <= k <= n. %C A363232 Explicit formulas for columns k=0,1,2,3,4 are given in the Butler-Markowsky link. %H A363232 K. K.-H. Butler and G. Markowsky, <a href="https://www.koreascience.or.kr/article/JAKO197225748110925.pdf">The Number of Maximal Subgroups of the Semigroup of Binary Relations</a>, Kyungpook Math. J. Vol 12, June 1972. %e A363232 Triangle begins: %e A363232 1; %e A363232 1, 1; %e A363232 1, 7, 3; %e A363232 1, 37, 66, 19; %e A363232 1, 175, 975, 990, 219; %e A363232 1, 781, 12090, 32575, 23345, 4231; %e A363232 1, 3367, 135903, 866550, 1514610, 814903, 130023; %e A363232 ... %Y A363232 Cf. A121337 (row sums), A001035 (main diagonal), A005061 (column k=1). %K A363232 nonn,tabl,more %O A363232 0,5 %A A363232 _Geoffrey Critzer_, May 22 2023