0,2

P = A136220 is a triangular matrix where column k of P^3 equals column 0 of P^(3k+3) such that column 0 of P^3 equals column 0 of P shift one place left.

(PARI) {a(n)=local(P=Mat(1), U, PShR); if(n==0, 1, for(i=0, n+2, PShR=matrix(#P, #P, r, c, if(r>=c, if(r==c, 1, if(c==1, 0, P[r-1, c-1])))); U=P*PShR^2; U=matrix(#P+1, #P+1, r, c, if(r>=c, if(r<#P+1, U[r, c], if(c==1, (P^3)[ #P, 1], (P^(3*c-1))[r-c+1, 1])))); P=matrix(#U, #U, r, c, if(r>=c, if(r<#U, P[r, c], (U^c)[r-c+1, 1])))); P[n+4, 4])}

Cf. A136220 (P), A136228 (U); other columns of P: A136221, A136222, A136223.

Adjacent sequences: A136221 A136222 A136223 this_sequence A136225 A136226 A136227

Sequence in context: A131765 A132864 A052700 this_sequence A009533 A135906 A002690

nonn

Paul D. Hanna (pauldhanna(AT)juno.com), Dec 25 2007