A128954 a(n) is equal to the number of positive integers m less than or equal to 10^n such that m is not divisible by the prime 2 and is not divisible by at least one of the primes 3, 5 and 7.

50, 495, 4952, 49524, 495238, 4952381, 49523810, 495238095, 4952380952, 49523809524, 495238095238, 4952380952381, 49523809523810, 495238095238095, 4952380952380952, 49523809523809524, 495238095238095238

Offset

2,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 2..1000

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Formula

a(n) = 10^n - floor(10^n/2) - floor(10^n/105) + floor(10^n/210).

Example

a(6) = 10^6 - floor(10^6/2) - floor(10^6/105) + floor(10^6/210) = 1000000 - floor(500000) - floor(9523.809...) + floor(4761.904...) = 1000000 - 500000 - 9523 + 4761 = 495238. - Jon E. Schoenfield, Nov 18 2018

Maple

f := n->10^n-floor(10^n/2)-floor(10^n/105)+floor(10^n/210);

Prog

(Magma) [10^n-Floor(10^n/2)-Floor(10^n/105)+Floor(10^n/210): n in [2..20]]; // Vincenzo Librandi, Oct 02 2011

Crossrefs

Cf. A092695.

Sequence in context: A019561 A164757 A189415 * A022147 A285044 A187669

Adjacent sequences: A128951 A128952 A128953 * A128955 A128956 A128957

Keyword

nonn

Author

Milan Janjic, Apr 28 2007

Status

approved