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 A086906 #13 Jun 17 2025 21:54:59 %S A086906 1,4,32,496,14172,816684,87982904,18748545824,7565600671504, %T A086906 5940152086634096 %N A086906 Number of symmetric singular n X n (0,1) matrices over the reals. %F A086906 a(n) = 2^(n*(n+1)/2) - A086899(n). %Y A086906 Cf. A046747, A086899, A086879, A086900, A118989, A118990, A118991, A118996, A119008, A119010. %Y A086906 Cf. A006125. %K A086906 nonn,more %O A086906 1,2 %A A086906 Yuval Dekel (dekelyuval(AT)hotmail.com), Sep 19 2003 %E A086906 _W. Edwin Clark_ computed the first entries. %E A086906 a(6)-a(7) from _Giovanni Resta_, May 08 2006 %E A086906 a(8)-a(10) from _Max Alekseyev_, Jun 17 2025