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 A086922 #22 Jun 25 2020 05:27:45 %S A086922 1,2,8,50,452,5682,96608,2185738,65108492 %N A086922 Number of idempotent n X n (0,1) matrices over the reals. %C A086922 From _Torlach Rush_, Jun 18 2020: (Start) %C A086922 Let m(n,k) be the number of idempotent n X n (0,1) matrices with k entries equal to 1. Then: %C A086922 k | m(n,k) %C A086922 -----|------------------------------------------------------ %C A086922 0 | 1 %C A086922 1 | n %C A086922 2 | A028895(n - 1) %C A086922 3 | 19 * A000292(n - 2) %C A086922 4 | ((n - 3) (n - 2) (n - 1) (35 n - 124))/8 %C A086922 5 | ((n - 4) (n - 3) (n - 2) (n - 1) (631 n - 2675))/120 %C A086922 ... %C A086922 Conjecture: There is no closed form expression for this sequence. %C A086922 (End) %Y A086922 Cf. A000292, A028895, A132186, A222821. %K A086922 nonn,more %O A086922 0,2 %A A086922 Yuval Dekel (dekelyuval(AT)hotmail.com), Sep 19 2003 %E A086922 a(5)-a(6) from _Torlach Rush_, Jun 17 2020 %E A086922 a(7)-a(8) from A222821 added by _Giovanni Resta_, Jun 23 2020