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A229837
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Decimal expansion of Sum_{n>=1} 1/(n*n!).
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11
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1, 3, 1, 7, 9, 0, 2, 1, 5, 1, 4, 5, 4, 4, 0, 3, 8, 9, 4, 8, 6, 0, 0, 0, 8, 8, 4, 4, 2, 4, 9, 2, 3, 1, 8, 3, 7, 9, 7, 4, 9, 0, 1, 2, 4, 5, 7, 9, 2, 7, 8, 3, 9, 9, 2, 8, 4, 0, 4, 6, 1, 1, 9, 6, 9, 9, 7, 6, 4, 6, 1, 0, 7, 7, 5, 6, 1, 3, 9, 4, 8, 2, 6, 1, 1, 9, 5, 3, 6, 4, 6, 8, 3, 4, 3, 9, 2, 2, 0, 7
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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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Sum_{n >= 1} 1/(n*n!) = Ei(1)-gamma where Ei is the exponential integral and gamma is Euler's constant.
Also pFq(1,1; 2,2; 1) where pFq is the generalized hypergeometric function.
Also li(e)-gamma, e being the Euler constant (A001113) and li the logarithmic integral function. - Stanislav Sykora, May 09 2015
Continued fraction expansion: Ei(1) - gamma = 1/(1 - 1^3/(5 - 2^3/(11 -...-(n-1)^3/(n^2+n-1) -...))). See A061572. - Peter Bala, Feb 01 2017
Equals Sum_{k>=1} H(k)*k/(k+1)!, where H(k) = A001008(k)/A002805(k) is the k-th harmonic number.
Equals Integral_{x=0..1} (exp(x) - 1)/x dx.
Equals -Integral_{x=0..1} exp(x)*log(x) dx.
Equals -Integral_{x=1..e} log(log(x)) dx. (End)
Equals e * Sum_{k>=1} (-1)^(k+1)*H(k)/k!, where H(k) = A001008(k)/A002805(k) is the k-th harmonic number. - Amiram Eldar, Jun 25 2021
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EXAMPLE
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1.3179021514544038948600088442492318379749012457927839928404611969976461...
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MAPLE
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MATHEMATICA
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RealDigits[ ExpIntegralEi[1] - EulerGamma, 10, 100] // First
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PROG
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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