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 A118989 #10 Jun 18 2025 18:03:26 %S A118989 1,3,25,271,6881,254911,20903681,2725061631,771426498049 %N A118989 Number of symmetric n X n (0,1)-matrices over the reals with zero permanent. %F A118989 a(n) = 2^(n*(n+1)/2) - A118991(n) = 2^A000217(n) - A118991(n) = A006125(n+1) - A118991(n). - _Max Alekseyev_, Apr 22 2010; corrected by Herman Jamke (hermanjamke(AT)fastmail.fm), Sep 26 2010 %Y A118989 Cf. A086906, A088672, A118986, A118991, A119009, A119010. %K A118989 nonn,more %O A118989 1,2 %A A118989 _Giovanni Resta_, May 08 2006 %E A118989 a(8)-a(9) from _Max Alekseyev_, Jun 18 2025