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 A118997 #12 Jun 17 2025 22:09:16 %S A118997 1,4,16,80,8448,907904,81949952,13480664064,12792558313472, %T A118997 18963201072750592 %N A118997 Number of real n X n symmetric (+1,-1) matrices with negative determinant. %F A118997 a(2n+1) = A118994(2n+1) = A118992(2n+1)/2. - _Max Alekseyev_, May 08 2009 %F A118997 a(n) = A118992(n) - A118994(n). - _Max Alekseyev_, Jun 12 2025 %Y A118997 Cf. A118999, A118992, A118994, A118996, A119000. %K A118997 nonn,more %O A118997 1,2 %A A118997 _Giovanni Resta_, May 08 2006 %E A118997 a(8)-a(10) from _Max Alekseyev_, Jun 17 2025