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A068566
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Numerator of Sum_{k=1..n} 1/(k * 2^k).
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3
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1, 5, 2, 131, 661, 1327, 1163, 148969, 447047, 44711, 983705, 7869871, 102309709, 204620705, 31972079, 32739453941, 556571077357, 556571247527, 10574855234543, 42299423848079, 42299425233749, 84598851790183
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OFFSET
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1,2
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COMMENTS
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Sum_{k>=1} 1/(k * 2^k) = log(2).
(Link) page 9:
T0 = 1/2 = 1/2
T1 = 1/2 + 1/8 = 5/8
T2 = 5/8 + 1/24 = 2/3
T3 = 2/3 + 1/64 = 131/192
T4 = 131/192 + 1/160 = 661/960
(T5 = 661/960 + 1/384 = 1327/1920)
... .
a(n)/A068565(n) is the first and the third column.
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LINKS
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FORMULA
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Integral_{x = 0..1} x^n/(1 + x)^(n+1) dx = log(2) - Sum_{k = 1..n} 1/(k * 2^k).
Hence a(n) = the numerator of Integral_{x = 0..1} ((1 + x)^n - x^n)/(1 + x)^(n+1) dx.
Integral_{x = 0..1/2} x^n/(1 - x) dx = Integral_{x >= 2} 1/(x^(n+2) - x^(n+1)) dx = log(2) - a(n)/A068565(n). (End)
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MAPLE
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map(numer, ListTools:-PartialSums([seq(1/k/2^k, k=1..100)])); # Robert Israel, Jul 10 2015
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MATHEMATICA
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Numerator[Accumulate[Table[1/(k 2^k), {k, 30}]]] (* Harvey P. Dale, May 11 2013 *)
a[n_]:=Log[2]-Hypergeometric2F1[1+n, 1+n, 2+n, -1]/(1+n);
Numerator[Table[Simplify[a[n]], {n, 1, 30}]] (* Gerry Martens, Aug 06 2015 *)
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PROG
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(PARI) vector(30, n, numerator(sum(k=1, n, 1/(k * 2^k)))) \\ Michel Marcus, Aug 07 2015
(Magma) [Numerator( (&+[1/(2^k*k): k in [1..n]]) ): n in [1..30]]; // G. C. Greubel, Jun 30 2019
(Sage) [numerator( sum(1/(2^k*k) for k in (1..n)) ) for n in (1..30)] # G. C. Greubel, Jun 30 2019
(GAP) List([1..30], n-> NumeratorRat( Sum([1..n], k-> 1/(2^k*k)) ) ) # G. C. Greubel, Jun 30 2019
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CROSSREFS
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KEYWORD
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easy,frac,nonn
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AUTHOR
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STATUS
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approved
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