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A370509
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Expansion of Sum_{k>=0} k! * ( x * (1+x^2) )^k.
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2
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1, 1, 2, 7, 28, 138, 818, 5658, 44784, 399366, 3962256, 43289760, 516432984, 6679346280, 93091875120, 1390851720840, 22175338353120, 375794883339120, 6745177713093840, 127830886641354960, 2550687440585679360, 53451172032327664560, 1173650135526055272960
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) = Sum_{k=0..floor(n/3)} (n-2*k)! * binomial(n-2*k,k).
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PROG
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(PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=0, N, k!*(x*(1+x^2))^k))
(PARI) a(n) = sum(k=0, n\3, (n-2*k)!*binomial(n-2*k, k));
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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