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A166903
Column 3 of triangle A166900.
4
1, 16, 230, 3564, 61845, 1207696, 26415840, 642448632, 17240108314, 506777596248, 16210958231104, 560988459704192, 20891752852722701, 833382707754108896, 35461362393617267808, 1603581518693484768464
OFFSET
0,2
COMMENTS
Triangle A166900 transforms rows into diagonals in the table of coefficients of successive iterations of x+x^2 (cf. A122888).
PROG
(PARI) {a(n)=local(F=x, M, N, P); M=matrix(n+5, n+5, r, c, F=x; for(i=1, r+c-2, F=subst(F, x, x+x^2+x*O(x^(n+5)))); polcoeff(F, c)); N=matrix(n+4, n+4, r, c, F=x; for(i=1, r, F=subst(F, x, x+x^2+x*O(x^(n+5)))); polcoeff(F, c)); P=matrix(n+4, n+4, r, c, M[r+1, c]); (P~*N~^-1)[n+4, 4]}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 27 2009
STATUS
approved