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.
%I A114601 #17 Aug 18 2025 14:35:14
%S A114601 1,3,23,393,13089,737595,58969079
%N A114601 Number of n X n symmetric positive definite matrices with 2's on the main diagonal and -1, 0, or 1 elsewhere.
%C A114601 This gives the number of different values of A + A' where A runs through the matrices counted in A086215.
%o A114601 (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) ) ) }
%o A114601 { a(n) = local(M,r,m); M=matrix(n,n,i,j,2*(i==j)); r=0; m=n; b(1); r }
%Y A114601 Cf. A086215, A085657.
%K A114601 hard,nonn,more
%O A114601 1,2
%A A114601 _Max Alekseyev_, Dec 13 2005, Nov 09 2006