0,2

Equals column 2 of triangle P=A135880:

1;

1, 1;

2, 2, 1;

6, 7, 3, 1;

25, 34, 15, 4, 1;

138, 215, 99, 26, 5, 1;

970, 1698, 814, 216, 40, 6, 1;

8390, 16220, 8057, 2171, 400, 57, 7, 1; ...

where column k of P^2 equals column 0 of P^(2k+2)

such that column 0 of P^2 equals column 0 of P shift left.

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

Cf. A135880; other columns: A135881, A135882, A135884.

Sequence in context: A156106 A111546 A152402 this_sequence A147664 A074521 A074536

Adjacent sequences: A135880 A135881 A135882 this_sequence A135884 A135885 A135886

nonn

Paul D. Hanna (pauldhanna(AT)juno.com), Dec 15 2007