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A327683
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Expansion of Product_{k>0} (1+sqrt(1+4*x^k))/2.
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4
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1, 1, 0, 4, -5, 17, -40, 144, -459, 1517, -5111, 17747, -62074, 219292, -782602, 2816664, -10205754, 37203230, -136360106, 502219652, -1857659296, 6897983144, -25704335380, 96090440940, -360265425619, 1354343161419, -5103948546609, 19278502980063, -72972099256954
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OFFSET
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0,4
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LINKS
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FORMULA
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a(n) ~ -(-1)^n * c * 2^(2*n - 1) / (sqrt(Pi) * n^(3/2)), where c = Product_{k>=1} (1 + sqrt(1 + 4*(-1/4)^k))/2 = 0.52271977595412566689522667777276363119313248923... - Vaclav Kotesovec, May 06 2021
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MAPLE
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N:= 40:
P:= mul((1+sqrt(1+4*x^k))/2, k=1..N):
S:= series(P, x, N+1):
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MATHEMATICA
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nmax = 30; CoefficientList[Series[Product[(1+Sqrt[1+4*x^k])/2, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Sep 22 2019 *)
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PROG
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(PARI) N=66; x='x+O('x^N); Vec(prod(k=1, N, (1+sqrt(1+4*x^k))/2))
(PARI) N=66; x='x+O('x^N); Vec(prod(i=1, N, 1-sum(j=1, N\i, (-1)^j*binomial(2*j-2, j-1)*x^(i*j)/j)))
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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