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%I #11 Apr 25 2013 03:20:09
%S 1,2,8,64,924,21737,749684,33568376
%N Number of n X n symmetric positive semi-definite matrices with 2's on the main diagonal and 1's and 0's elsewhere.
%C Of course the total number of symmetric matrices of this type (not necessarily positive semi-definite) is 2^C(n,2).
%C This gives the number of different values of M + M' where M runs through the matrices counted in A038379. - Max Alekseyev, Nov 11 2006
%H <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>
%e The matrix
%e 2 0 0 0 1
%e 0 2 0 1 1
%e 0 0 2 1 1
%e 0 1 1 2 0
%e 1 1 1 0 2
%e is one of the 100 5 X 5 matrices which are not positive semi-definite.
%e Its eigenvalues are approximately [2., -0.135779205069857, 4.135779205069857, 1.337846553138044, 2.662153446861956]
%Y Cf. A085658, A080858, A083029.
%K nonn,more
%O 1,2
%A _N. J. A. Sloane_, Jul 12 2003
%E 3 more terms from _Max Alekseyev_, Nov 08 2006
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