A116427 The number of n-almost primes less than or equal to 6^n, starting with a(0)=1.

1, 3, 13, 50, 200, 726, 2613, 9061, 30779, 102637, 338230, 1102674, 3566001, 11455355, 36597558, 116395587, 368749900, 1164407829, 3666312894, 11515047829, 36085395700, 112857846859, 352329509934, 1098136237818

Offset

0,2

Links

Table of n, a(n) for n=0..23.

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[n, 6^n], {n, 21}]

Crossrefs

Cf. A078840, A078841, A078842, A116432, A078843, A116426, A078844, A116427, A078845, A116428, A116429, A116430, A078846, A116431.

Sequence in context: A284329 A259338 A196907 * A008827 A026529 A363881

Adjacent sequences: A116424 A116425 A116426 * A116428 A116429 A116430

Keyword

nonn

Author

Robert G. Wilson v, Feb 10 2006

Extensions

a(22)-a(23) from Donovan Johnson, Oct 01 2010

Status

approved