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A330255
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Expansion of e.g.f. Sum_{k>=1} (cosh(x^k) - 1) (even powers only).
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4
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1, 13, 361, 21841, 1814401, 260124481, 43589145601, 11333696774401, 3210079038566401, 1317822591538252801, 562000363888803840001, 336953340897297630105601, 201645730563302817792000001, 165147853334842304408401920001, 132994909752412012763531673600001
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OFFSET
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1,2
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LINKS
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FORMULA
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E.g.f.: Sum_{k>=1} x^(2*k) / ((2*k)! * (1 - x^(2*k))) (even powers only).
a(n) = (2*n)! * Sum_{d|n} 1 / (2*d)!.
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MATHEMATICA
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nmax = 15; Table[(CoefficientList[Series[Sum[Cosh[x^k] - 1, {k, 1, nmax}], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}] // Rest
Table[(2 n)! DivisorSum[n, 1/(2 #)! &], {n, 1, 15}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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