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A127396
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Number of 3-almostprimes <= 2^n.
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3
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0, 0, 1, 2, 7, 13, 30, 60, 125, 256, 513, 1049, 2082, 4214, 8401, 16771, 33427, 66550, 132405, 262865, 522296, 1036033, 2055256, 4075039, 8078110, 16008485, 31720903, 62847087, 124501149, 246638355, 488559079, 967785236, 1917099175, 3797688543
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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LINKS
| Robert G. Wilson v, Table of n, a(n) for n = 1..49
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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FORMULA
| a(n) = A072114(2^n). - R. J. Mathar, Aug 26 2011
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MATHEMATICA
| ThreeAlmostPrimePi[n_] := Sum[PrimePi[n/(Prime@i*Prime@j)] - j + 1, {i, PrimePi[n^(1/3)]}, {j, i, PrimePi[Sqrt[n/Prime@i]]}]; Table[ ThreeAlmostPrimePi[2^n], {n, 30}]
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CROSSREFS
| Cf. A126279, A109251, A125527.
Sequence in context: A180470 A183435 A141777 * A079119 A051748 A086904
Adjacent sequences: A127393 A127394 A127395 * A127397 A127398 A127399
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KEYWORD
| nonn,less
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 29 2006
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