1,2
This gives the number of different values of A + A' where A runs throgh the matrices counted in A086215.
(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) ) ) }
Cf. A086215, A085657.
Sequence in context: A092664 A073588 A068338 * A178315 A118195 A055326
Adjacent sequences: A114598 A114599 A114600 * A114602 A114603 A114604
hard,nonn,more
Max Alekseyev (maxale(AT)gmail.com), Dec 13 2005, Nov 09 2006
