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A166886
Column 2 of triangle A166884.
3
1, 2, 9, 62, 593, 7266, 108720, 1922166, 39212154, 906623004, 23429034168, 669203550906, 20935080981744, 711872134399868, 26142553369667634, 1031146768716808794, 43475757877044427198, 1951261759908828697902
OFFSET
1,2
COMMENTS
Triangle A166884 transforms diagonals in the triangle A166880 of coefficients in the successive iterations of x+x^2+x^3.
PROG
(PARI) {a(n)=local(F=x, M, N, P, m=n+1); M=matrix(m+2, m+2, r, c, F=x; for(i=1, r+c-2, F=subst(F, x, x+x^2+x^3+x*O(x^(m+2)))); polcoeff(F, c)); N=matrix(m+1, m+1, r, c, M[r, c]); P=matrix(m+1, m+1, r, c, M[r+1, c]); (P~*N~^-1)[n+2, 2]}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 21 2009
STATUS
approved