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%I #2 Mar 30 2012 18:37:18
%S 1,4,21,156,1540,19160,288813,5123608,104657520,2420186616,
%T 62514944778,1784255891484,55767065855228,1894463658611680,
%U 69504774168222109,2738952451360200312,115380142451625516088,5174227834995200591840
%N Column 1 of triangle A166900.
%C Triangle A166900 transforms rows into diagonals in the table of coefficients of successive iterations of x+x^2 (cf. A122888).
%o (PARI) {a(n)=local(F=x, M, N, P); M=matrix(n+3, n+3, r, c, F=x;for(i=1, r+c-2, F=subst(F, x, x+x^2+x*O(x^(n+3)))); polcoeff(F, c)); N=matrix(n+2, n+2, r, c, F=x;for(i=1, r, F=subst(F, x, x+x^2+x*O(x^(n+3)))); polcoeff(F, c)); P=matrix(n+2, n+2, r, c, M[r+1, c]); (P~*N~^-1)[n+2, 2]}
%Y Cf. A166900, A166902, A166903, A122888, A135080.
%K nonn
%O 0,2
%A _Paul D. Hanna_, Nov 27 2009
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