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; b(1); r } { b(k) = if(k>n, 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 this_sequence A118195 A055326 A133338

Adjacent sequences: A114598 A114599 A114600 this_sequence A114602 A114603 A114604

hard,nonn

Max Alekseyev (maxal(AT)cs.ucsd.edu), Dec 13 2005, Nov 09 2006