A128951 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 5 and is not divisible by at least one of the primes 2, 3 and 7.

78, 781, 7809, 78096, 780952, 7809524, 78095238, 780952381, 7809523809, 78095238096, 780952380952, 7809523809524, 78095238095238, 780952380952381, 7809523809523809, 78095238095238096, 780952380952380952

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/5) - floor(10^n/42) + floor(10^n/210).

Example

a(6) = 10^6 - floor(10^6/5) - floor(10^6/42) + floor(10^6/210) = 1000000 - floor(200000) - floor(23809.523...) + floor(4761.904...) = 1000000 - 200000 - 23809 + 4761 = 780952.

Maple

f := n->10^n-floor(10^n/5)-floor(10^n/42)+floor(10^n/210);

Mathematica

Table[With[{c=10^n}, c-Floor[c/5]-Floor[c/42]+Floor[c/210]], {n, 2, 20}] (* Harvey P. Dale, Nov 02 2019 *)

Prog

(Magma) [10^n-Floor(10^n/5)-Floor(10^n/42)+Floor(10^n/210): n in [2..20]]; // Vincenzo Librandi, Oct 02 2011

Crossrefs

Cf. A092695.

Sequence in context: A297759 A147619 A119093 * A370209 A272383 A027786

Adjacent sequences: A128948 A128949 A128950 * A128952 A128953 A128954

Keyword

nonn

Author

Milan Janjic, Apr 28 2007

Extensions

Example edited by Jon E. Schoenfield, Nov 18 2018

Status

approved