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 A081080 #5 Dec 21 2017 14:30:20 %S A081080 2,4,10,38,194,1378,13570,188546,3664898 %N A081080 Number of n X n ortho-projection matrices over GF(2). Also, the number of labeled ortho-projection graphs on n vertices. %C A081080 A matrix over GF(2) is an ortho-projection if and only if the matrix is symmetric and idempotent. A labeled ortho-projection graph is a labeled, undirected pseudograph without multiple edges and without multiple loops whose adjacency matrix is an ortho-projection matrix over GF(2). These matrices and graphs arise naturally in low-dimensional topology. %D A081080 B. Shtylla and L. Zulli, Ortho-projection graphs, in preparation. %H A081080 L. Zulli, <a href="http://www.cs.lafayette.edu/~zullil/">Home Page</a> [broken link] %e A081080 a(2)=4 because there are four 2 X 2 ortho-projection matrices over GF(2), namely [0 0 / 0 0], [0 0 / 0 1], [1 0 / 0 0], [1 0 / 0 1]. %Y A081080 Cf. A081081, A081082. %K A081080 hard,more,nonn %O A081080 1,1 %A A081080 B. Shtylla and L. Zulli (shtyllab(AT)lafayette.edu, zullil(AT)lafayette.edu), Mar 05 2003 %E A081080 a(9) from Louis Zulli (zullil(AT)lafayette.edu), Aug 23 2004