login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A120049 Number of 8-almost primes less than or equal to 10^n. 12
0, 0, 0, 7, 105, 1418, 17572, 207207, 2367507, 26483012, 291646797, 3173159326, 34192782745, 365561221293, 3882841742380 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..14.

EXAMPLE

There are 7 eight-almost primes up to 1000: 256, 384, 576, 640, 864, 896 & 960.

MATHEMATICA

AlmostPrimePi[k_Integer, n_] := Module[{a, i}, a[0] = 1; If[k == 1, PrimePi[n], Sum[PrimePi[n/Times @@ Prime[Array[a, k - 1]]] - a[k - 1] + 1, Evaluate[ Sequence @@ Table[{a[i], a[i - 1], PrimePi[(n/Times @@ Prime[Array[a, i - 1]])^(1/(k - i + 1))]}, {i, k - 1}]]]]]; (* Eric W. Weisstein, Feb 07 2006 *)

Table[AlmostPrimePi[8, 10^n], {n, 12}]

CROSSREFS

Cf. A066265, A014613, A116382.

Cf. A006880, A036352, A109251, A114106, A114453, A120047, A120048, A120049, A120050, A120051, A120052, A120053, A116430.

Sequence in context: A098362 A093741 A139742 * A067420 A131869 A132867

Adjacent sequences:  A120046 A120047 A120048 * A120050 A120051 A120052

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Feb 07 2006

EXTENSIONS

a(13) and a(14) from Robert G. Wilson v, Jan 07 2007

Example corrected by Harvey P. Dale, Aug 13 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 17 21:35 EST 2020. Contains 332006 sequences. (Running on oeis4.)