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%I #2 Mar 30 2012 18:37:18
%S 1,3,18,157,1812,25989,445255,8865333,201058614,5114874693,
%T 144207579708,4462151144553,150316762118466,5475746846833734,
%U 214463847533104125,8986421286160678944,401112805593137715609,18999650382886046745879
%N Column 3 of triangle A166884.
%C Triangle A166884 transforms diagonals in the triangle A166880 of coefficients in the successive iterations of x+x^2+x^3.
%o (PARI) {a(n)=local(F=x, M, N, P, m=n+2); 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+3, 3]}
%Y Cf. A166880, A166884, A166885, A166886.
%K nonn
%O 1,2
%A _Paul D. Hanna_, Nov 21 2009
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