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A215712
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Numerator of sum(i=1..n, 3*i/4^i )
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2
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3, 9, 81, 21, 1359, 2727, 21837, 21843, 349515, 699045, 5592393, 2796201, 89478471, 178956963, 1431655749, 1431655761, 22906492227, 45812984481, 366503875905, 22906492245, 5864062014783, 11728124029599, 93824992236861, 93824992236879, 1501199875790139
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OFFSET
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1,1
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COMMENTS
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The limit as n goes to infinity is 4/3.
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REFERENCES
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Calvin C. Clawson, The Beauty and Magic of Numbers. New York: Plenum Press (1996): 96.
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..1000
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EXAMPLE
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a(4) = 21 because 3/4 + 6/16 + 9/64 + 12/256 = 3/4 + 3/8 + 9/64 + 3/64 = 48/64 + 24/64 + 9/64 + 3/64 = 84/64 = 21/16.
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MATHEMATICA
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Table[Numerator[Sum[3i/4^i, {i, n}]], {n, 40}]
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PROG
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(Magma) [Numerator(&+[3*i/4^i: i in [1..n]]): n in [1..25]]; // Bruno Berselli, Sep 03 2012
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CROSSREFS
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Cf. A215713 for the denominators.
A036295/A036296 is the same with i/2^i instead of 3i/4^i.
Cf. A122553.
Sequence in context: A032330 A018604 A301535 * A000218 A139731 A259986
Adjacent sequences: A215709 A215710 A215711 * A215713 A215714 A215715
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KEYWORD
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nonn,easy,frac
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AUTHOR
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Alonso del Arte, Aug 21 2012
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EXTENSIONS
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a(17) corrected by Vincenzo Librandi, Sep 04 2012
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STATUS
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approved
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