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%I #4 Dec 09 2012 02:29:03
%S 1,9,177,9800,1131750,225598527,69153712446,30211650109440,
%T 17832410391617082,13670065258130703125,13203133188522251881137,
%U 15685246720965582029887488,22477297594725738707224270105,38231902029181930196176183861755,76144787589417130318451646093750000
%N Main diagonal of triangle A220265.
%C G.f. of row n of triangle A220265 equals: Sum_{k=0..n^2-n+1} A220265(n,k)*y^k = (2*(1+y)^n - 1)*((1+y)^n - 1)^(n-1)/y^(n-1) for n>=1.
%F a(n) = A220265(n,n-1) for n>=1.
%e Irregular triangle A220265 begins:
%e 1, 2;
%e 2, 9, 8, 2;
%e 9, 72, 177, 222, 163, 72, 18, 2;
%e 64, 800, 3696, 9800, 17408, 22284, 21340, 15554, 8652, 3633, 1120, 240, 32, 2;
%e 625, 11250, 82500, 365000, 1131750, 2654250, 4922750, 7425000, 9274150, 9704600, 8566200, 6398000, 4042345, 2152890, 959690, 354020, 106251, 25300, 4600, 600, 50, 2; ...
%o (PARI) {a(n)=polcoeff((2*(1+x)^n-1)*((1+x)^n-1)^(n-1)/x^(n-1), n-1)}
%o for(n=1, 20, print1(a(n), ", "))
%Y Cf. A220265, A220266.
%K nonn
%O 1,2
%A _Paul D. Hanna_, Dec 09 2012
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