This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A120048 Number of 7-almost primes less than or equal to 10^n. 10
 0, 0, 0, 14, 231, 2973, 35585, 409849, 4600247, 50678212, 550454756, 5913771637, 62981797962, 665997804082, 7001087934965 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS EXAMPLE There are 14 seven-almost primes up to 1000: 128, 192, 288, 320, 432, 448, 480, 648, 672, 704, 720, 800, 832 & 972. 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[7, 10^n], {n, 11}] CROSSREFS Cf. A066265, A014613, A116382. Cf. A006880, A036352, A109251, A114106, A114453, A120047, A120048, A120049, A120050, A120051, A120052, A120053, A116430. Sequence in context: A027774 A099272 A273625 * A079563 A230346 A280559 Adjacent sequences:  A120045 A120046 A120047 * A120049 A120050 A120051 KEYWORD nonn AUTHOR Robert G. Wilson v, Feb 07 2006 EXTENSIONS More terms from Robert G. Wilson v, Jan 07 2007 Example corrected by Harvey P. Dale, Jan 25 2013 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.

Last modified October 17 19:24 EDT 2019. Contains 328127 sequences. (Running on oeis4.)