|
%I #18 Sep 08 2022 08:45:30
%S 66,657,6572,65715,657143,6571429,65714286,657142857,6571428572,
%T 65714285715,657142857143,6571428571429,65714285714286,
%U 657142857142857,6571428571428572,65714285714285715,657142857142857143
%N 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 3 and is not divisible by at least one of the primes 2, 5 and 7.
%H Vincenzo Librandi, <a href="/A128952/b128952.txt">Table of n, a(n) for n = 2..1000</a>
%H Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas for Some Functions on Finite Sets</a>
%F a(n) = 10^n - floor(10^n/3) - floor(10^n/70) + floor(10^n/210).
%e a(6) = 10^6 - floor(10^6/3) - floor(10^6/70) + floor(10^6/210) = 1000000 - floor(333333.333...) - floor(14285.714...) + floor(4761.904...) = 1000000 - 333333 - 14285 + 4761 = 657143. - _Jon E. Schoenfield_, Nov 18 2018
%p a := n->10^n-floor(10^n/3)-floor(10^n/70)+floor(10^n/210);
%t Table[With[{c=10^n},c-Floor[c/3]-Floor[c/70]+Floor[c/210]],{n,2,20}] (* _Harvey P. Dale_, Jun 22 2022 *)
%o (Magma) [10^n-Floor(10^n/3)-Floor(10^n/70)+Floor(10^n/210): n in [2..20]]; // _Vincenzo Librandi_, Oct 02 2011
%Y Cf. A092695.
%K nonn
%O 2,1
%A _Milan Janjic_, Apr 28 2007
| 