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A diagonal of triangle A185755.
4

%I #10 Feb 01 2025 14:54:37

%S 2,15,120,1190,14595,215950,3761310,75550188,1721103648,43872089118,

%T 1237592664451,38282002057156,1288537309627464,46886217384094764,

%U 1834003542264708444,76744318019878844916,3420833746251201921980

%N A diagonal of triangle A185755.

%C A185755(n,k) equals the coefficient of x^n*y^k in the n-th iteration of x*(1+xy)/(1-x).

%o (PARI) {a(n)=local(A=x, G=x*(1+x*y)/(1-x)); for(i=1, n+1, A=subst(G, x, A+O(x^(n+2))));polcoeff(polcoeff(A, n+1,x),n-1,y)}

%Y Cf. A185755, A185756, A185757, A185759.

%K nonn,changed

%O 1,1

%A _Paul D. Hanna_, Feb 03 2011