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Search: id:A120035
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| A120035 |
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Number of 4-almost primes 4ap such that 2^n < 4ap <= 2^(n+1). |
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+0
11
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| 0, 0, 0, 1, 1, 5, 7, 20, 37, 81, 173, 344, 736, 1461, 3065, 6208, 12643, 25662, 52014, 105487, 212566, 430007, 865650, 1744136, 3508335, 7053390, 14167804, 28441899, 57065447, 114418462, 229341261, 459442819, 920097130, 1841946718, 3686197728
(list; graph; listen)
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OFFSET
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0,6
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COMMENT
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The partial sum equals the number of Pi_4(2^n).
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EXAMPLE
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(2^4, 2^5] there is one semiprime, namely 24. 16 was counted in the previous entry.
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MATHEMATICA
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FourAlmostPrimePi[n_] := Sum[ PrimePi[n/(Prime@i*Prime@j*Prime@k)] - k + 1, {i, PrimePi[n^(1/4)]}, {j, i, PrimePi[(n/Prime@i)^(1/3)]}, {k, j, PrimePi@Sqrt[n/(Prime@i*Prime@j)]}]; t = Table[ FourAlmostPrimePi[2^n], {n, 0, 37}]; Rest@t - Most@t
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CROSSREFS
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Cf. A014613, A114106, A036378, A120033, A120034, A120035, A120036, A120037, A120038, A120039, A120040, A120041, A120042, A120043.
Sequence in context: A062654 A130729 A117321 this_sequence A091154 A057424 A027152
Adjacent sequences: A120032 A120033 A120034 this_sequence A120036 A120037 A120038
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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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