%I #2 Mar 30 2012 18:37:20

%S 1,2,14,174,3102,72090,2066073,70420126,2782399406,125043232266,

%T 6298621761335,351484024822788,21523422229105305,1434943982960717580,

%U 103463060233836392794,8022156135358465396630,665603454632822500855294

%N Coefficients of x^n in the (n-1)-th iteration of x/(1-x)^2 for n>=1.

%e Let F_n(x) denote the n-th iteration of F(x) = x/(1-x)^2;

%e then coefficients in the successive iterations of F(x) begin:

%e F_0: [(1), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...];

%e F(x):[1, (2), 3, 4, 5, 6, 7, 8, 9, 10, 11, ...];

%e F_2: [1, 4, (14), 46, 145, 444, 1331, 3926, 11434, 32960, ...];

%e F_3: [1, 6, 33, (174), 892, 4480, 22149, 108144, 522685, ...];

%e F_4: [1, 8, 60, 436, (3102), 21728, 150350, 1030158, 7000917, ...];

%e F_5: [1, 10, 95, 880, 8015, (72090), 642031, 5671962, ...];

%e F_6: [1, 12, 138, 1554, 17255, 189596, (2066073), 22361904, ...];

%e F_7: [1, 14, 189, 2506, 32830, 426244, 5494797, (70420126),...];

%e F_8: [1, 16, 248, 3784, 57132, 855840, 12740700, 188692708, (2782399406), ...]; ...

%e where the coefficients along the diagonal (shown in parenthesis)

%e form the initial terms of this sequence.

%o (PARI) {a(n)=local(F=x/(1-x+x*O(x^n))^2, G=x+x*O(x^n)); if(n<1, 0, for(i=1, n-1, G=subst(F, x, G)); return(polcoeff(G, n, x)))}

%Y Cf. A119821, A119820.

%K nonn

%O 0,2

%A _Paul D. Hanna_, Oct 28 2009