cp's OEIS Frontend

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.

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

Original entry on oeis.org

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

Views

Author

Max Alekseyev, Dec 13 2005, Nov 09 2006

Keywords

Comments

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

Crossrefs

Programs

  • PARI
    { 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) ) ) }
    { a(n) = local(M,r,m); M=matrix(n,n,i,j,2*(i==j)); r=0; m=n; b(1); r }