A100752 a(n) is the number of positive integers <= 10^n that are divisible by no prime exceeding 3.

1, 7, 20, 40, 67, 101, 142, 190, 244, 306, 376, 452, 534, 624, 720, 824, 935, 1052, 1178, 1309, 1447, 1593, 1745, 1905, 2071, 2244, 2424, 2611, 2806, 3006, 3214, 3429, 3652, 3881, 4117, 4360, 4610, 4866, 5131, 5401, 5679, 5964, 6255, 6553, 6859, 7172, 7491

Offset

0,2

Comments

A good approximation seems to be ceiling(log(10^n)*log(6*10^n)/(log(3)*log(4))). - Horst H. Manninger, Oct 29 2022

Links

David A. Corneth, Table of n, a(n) for n = 0..1999

Example

a(1) = 7 as there are 7 3-smooth numbers less than 10^1 = 10; they are 1, 2, 3, 4, 6, 8, 9. - David A. Corneth, Nov 14 2019

Mathematica

f[n_] := Sum[ Floor@ Log[2, n/3^i] + 1, {i, 0, Log[3, n]}]; Table[ f[10^n], {n, 0, 46}] (* Robert G. Wilson v, Nov 07 2012 *)

Crossrefs

Cf. A003586, A011557, A071521.

Cf. A066343, A106598, A106600, A107352, A106629.

Row 2 of A253635.

Sequence in context: A025056 A038349 A360226 * A162024 A143058 A298488

Adjacent sequences: A100749 A100750 A100751 * A100753 A100754 A100755

Keyword

nonn

Author

Robert G. Wilson v, May 27 2005

Status

approved