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 A038379 #20 Jun 23 2024 11:51:34
%S A038379 1,3,27,729,52649,9058475,3383769523,2520512534065
%N A038379 Number of real {0,1} n X n matrices A such that M = A + A' has 2's on the main diagonal, 0's and 1's elsewhere and is positive semi-definite.
%C A038379 Necessarily A has all 1's on the main diagonal.
%C A038379 A real matrix M is positive semi-definite if its eigenvalues are >= 0.
%C A038379 For n <= 4, a(n) equals the upper bound 3^C(n,2).
%C A038379 For the number of different values of symmetric parts A + A', see A085658. - _Max Alekseyev_, Nov 11 2006
%H A038379 <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>
%F A038379 a(n) = Sum_{k=0..C(n,2)} 2^k * A083029(n,k).
%Y A038379 Cf. A055165, which counts nonsingular {0, 1} matrices, A003024, which counts {0, 1} matrices with positive eigenvalues, A085656 (positive definite matrices).
%Y A038379 Cf. A085657, A085658, A080858, A083029.
%K A038379 nonn,more,nice
%O A038379 1,2
%A A038379 _N. J. A. Sloane_, Jul 13 2003
%E A038379 Definition corrected Nov 10 2006
%E A038379 a(6)-a(8) from _Max Alekseyev_, Nov 11 2006
%E A038379 Edited by _Max Alekseyev_, Jun 05 2024