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A116428 The number of n-almost primes less than or equal to 8^n, starting with a(0)=1. 8
1, 4, 22, 125, 669, 3410, 16677, 78369, 359110, 1612613, 7133274, 31185350, 135062165, 580556958, 2480278767, 10542976739, 44626102826, 188215850830, 791374442571 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..18.

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, 8^n], {n, 14}]

CROSSREFS

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

Sequence in context: A260346 A136777 A056625 * A121187 A011789 A047039

Adjacent sequences:  A116425 A116426 A116427 * A116429 A116430 A116431

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Feb 14 2006

EXTENSIONS

a(15)-a(18) from Donovan Johnson, Oct 01 2010

STATUS

approved

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Last modified September 24 22:46 EDT 2021. Contains 347651 sequences. (Running on oeis4.)