A114601 Number of n X n symmetric positive definite matrices with 2's on the main diagonal and -1, 0, or 1 elsewhere.

1, 3, 23, 393, 13089, 737595, 58969079

Offset

1,2

Comments

This gives the number of different values of A + A' where A runs through the matrices counted in A086215.

Links

Table of n, a(n) for n=1..7.

Prog

(PARI) { a(n) = M=matrix(n, n, i, j, 2*(i==j)); r=0; m=n; b(1); r } { b(k) = if(k>m, r++; return); forvec(x=vector(k-1, i, [-1, 1]), for(i=1, k-1, M[k, i]=M[i, k]=x[i]); if( matdet(vecextract(M, 2^k-1, 2^k-1), 1)>0, b(k+1) ) ) }

Crossrefs

Cf. A086215, A085657.

Sequence in context: A255881 A243195 A233218 * A178315 A210910 A280654

Adjacent sequences: A114598 A114599 A114600 * A114602 A114603 A114604

Keyword

hard,nonn,more

Author

Max Alekseyev, Dec 13 2005, Nov 09 2006

Status

approved