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 A220267 Main diagonal of triangle A220265. 1
 1, 9, 177, 9800, 1131750, 225598527, 69153712446, 30211650109440, 17832410391617082, 13670065258130703125, 13203133188522251881137, 15685246720965582029887488, 22477297594725738707224270105, 38231902029181930196176183861755, 76144787589417130318451646093750000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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. LINKS FORMULA a(n) = A220265(n,n-1) for n>=1. EXAMPLE Irregular triangle A220265 begins: 1, 2; 2, 9, 8, 2; 9, 72, 177, 222, 163, 72, 18, 2; 64, 800, 3696, 9800, 17408, 22284, 21340, 15554, 8652, 3633, 1120, 240, 32, 2; 625, 11250, 82500, 365000, 1131750, 2654250, 4922750, 7425000, 9274150, 9704600, 8566200, 6398000, 4042345, 2152890, 959690, 354020, 106251, 25300, 4600, 600, 50, 2; ... PROG (PARI) {a(n)=polcoeff((2*(1+x)^n-1)*((1+x)^n-1)^(n-1)/x^(n-1), n-1)} for(n=1, 20, print1(a(n), ", ")) CROSSREFS Cf. A220265, A220266. Sequence in context: A193443 A003711 A009009 * A304402 A034221 A034240 Adjacent sequences:  A220264 A220265 A220266 * A220268 A220269 A220270 KEYWORD nonn AUTHOR Paul D. Hanna, Dec 09 2012 STATUS approved

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Last modified May 22 22:13 EDT 2022. Contains 353959 sequences. (Running on oeis4.)