

A120034


Number of 3almost primes t such that 2^n < t <= 2^(n+1).


8



0, 0, 1, 1, 5, 6, 17, 30, 65, 131, 257, 536, 1033, 2132, 4187, 8370, 16656, 33123, 65855, 130460, 259431, 513737, 1019223, 2019783, 4003071, 7930375, 15712418, 31126184, 61654062, 122137206, 241920724, 479226157, 949313939, 1880589368, 3725662783
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OFFSET

0,5


COMMENTS

The partial sum equals the number of Pi_3(2^n) = A127396(n).


LINKS

Table of n, a(n) for n=0..34.


EXAMPLE

(2^3, 2^4] there is one semiprime, namely 12. 8 was counted in the previous entry.


MATHEMATICA

ThreeAlmostPrimePi[n_] := Sum[PrimePi[n/(Prime@i*Prime@j)]  j + 1, {i, PrimePi[n^(1/3)]}, {j, i, PrimePi@Sqrt[n/Prime@i]}]; t = Table[ ThreePrimePi[2^n], {n, 0, 35}]; Rest@t  Most@t


CROSSREFS

Cf. A014612, A072114, A109251, A036378, A120033  A120043.
Sequence in context: A041773 A041054 A297980 * A094425 A078981 A041555
Adjacent sequences: A120031 A120032 A120033 * A120035 A120036 A120037


KEYWORD

nonn


AUTHOR

Jonathan Vos Post and Robert G. Wilson v, Mar 20 2006


STATUS

approved



