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 A118991 #10 Jun 18 2025 18:03:42 %S A118991 1,5,39,753,25887,1842241,247531775,65994415105,34412945590783 %N A118991 Number of real n X n symmetric (0,1) matrices with nonzero permanent. %F A118991 a(n) = 2^(n(n+1)/2) - A118989(n) = 2^A000217(n) - A118989(n) = A006125(n+1) - A118989(n). - _Max Alekseyev_, Apr 22 2010; corrected by Herman Jamke (hermanjamke(AT)fastmail.fm), Sep 26 2010 %Y A118991 Cf. A086899, A118986, A118989, A118993, A119009. %K A118991 nonn,more %O A118991 1,2 %A A118991 _Giovanni Resta_, May 08 2006 %E A118991 a(8)-a(9) from _Max Alekseyev_, Jun 18 2025