A120044 The 10^n-th 3-almost prime.

8, 45, 412, 3918, 38991, 395085, 4046429, 41657362, 429891626, 4439956573, 45851698382, 473238120286, 4880292241955, 50280826966354

Offset

0,1

Links

Table of n, a(n) for n=0..13.

Mathematica

ThreeAlmostPrimePi[n_] := Sum[ PrimePi[n/(Prime@i*Prime@j)] - j + 1, {i, PrimePi[n^(1/3)]}, {j, i, PrimePi@ Sqrt[n/Prime@i]}]; ThreeAlmostPrime[n_] := Block[{e = Floor[Log[2, n]], a, b}, a = 2^e; Do[b = 2^p; While[ThreeAlmostPrimePi[a] < n, a = a + b]; a = a - b/2, {p, e, 0, -1}]; a + b/2]; Do[ Print@ThreeAlmostPrime[10^n], {n, 0, 13}]
ThreePrime[n_] := Block[{e = Floor[ Log[2, n] +2], a, b}, a = 2^e; Do[b = 2^p; While[ ThreePrimePi[a] < n, a = a + b]; a = a - b/2, {p, e, 0, -1}]; a + b/2]; Table[ ThreePrime[n], {n, 0, 13}]

Crossrefs

Cf. A109251, A006988, A114125, A120045, A120046.

Sequence in context: A367435 A006887 A009369 * A328885 A002686 A306047

Adjacent sequences: A120041 A120042 A120043 * A120045 A120046 A120047

Keyword

more,nonn

Author

Robert G. Wilson v, Feb 15 2006

Status

approved