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Search: id:A120033
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| A120033 |
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Number of semiprimes 2ap such that 2^n < 2ap <= 2^(n+1). |
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+0
13
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| 0, 1, 1, 4, 4, 12, 20, 40, 75, 147, 285, 535, 1062, 2006, 3918, 7548, 14595, 28293, 54761, 106452, 206421, 401522, 780966, 1520543, 2962226, 5777162, 11272279, 22009839, 43006972, 84077384, 164482781, 321944211, 630487562, 1235382703
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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The partial sum equals the number of Pi_2(2^n).
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EXAMPLE
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(2^2, 2^3] there is one semiprime, namely 6. 4 was counted in the previous entry.
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MATHEMATICA
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SemiPrimePi[n_] := Sum[PrimePi[n/Prime[i]] - i + 1, {i, PrimePi[Sqrt[n]]}]; t = Table[SemiPrimePi[2^n], {n, 0, 35}]; Rest@t - Most@t
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CROSSREFS
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Cf. A001358, A066265, A036378, A120033, A120034, A120035, A120036, A120037, A120038, A120039, A120040, A120041, A120042, A120043.
Sequence in context: A157617 A053415 A079902 this_sequence A097073 A019085 A106232
Adjacent sequences: A120030 A120031 A120032 this_sequence A120034 A120035 A120036
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KEYWORD
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nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com) and Robert G. Wilson v (rgwv(AT)rgwv.com), Mar 20 2006
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