A215712 Numerator of sum(i=1..n, 3*i/4^i ).
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
Offset: 1
Examples
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.
References
- Calvin C. Clawson, The Beauty and Magic of Numbers. New York: Plenum Press (1996): 96.
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Crossrefs
Programs
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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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Mathematica
Table[Numerator[Sum[3i/4^i, {i, n}]], {n, 40}]
Extensions
a(17) corrected by Vincenzo Librandi, Sep 04 2012
Comments