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 A084552 #8 Mar 14 2017 18:36:37 %S A084552 1,2,7,38,286,2686,28512,312572,3337588,40963216 %N A084552 Number of n X n symmetric positive definite matrices with 2's on the main diagonal and -1's and 0's elsewhere. %C A084552 Of course the total number of symmetric matrices of this type (not necessarily positive definite) is 2^C(n,2). %C A084552 This gives the number of different values of M + M' where M runs through the matrices counted in A127502. %H A084552 <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a> %e A084552 The singular matrix %e A084552 2 -1 -1 %e A084552 -1 2 -1 %e A084552 -1 -1 2 %e A084552 is the only 3 X 3 matrix of this type which is not positive definite. %Y A084552 Cf. A084553, A085659, A080858, A083029. %K A084552 nonn %O A084552 1,2 %A A084552 _N. J. A. Sloane_, Jul 13 2003 %E A084552 a(6)-a(10) from _Max Alekseyev_, Jan 16 2006