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A128957 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 at least one of the primes 2,5 and is not divisible by at least one of the primes 3,7. 1
86, 857, 8571, 85715, 857142, 8571429, 85714286, 857142857, 8571428571, 85714285715, 857142857142, 8571428571429, 85714285714286, 857142857142857, 8571428571428571, 85714285714285715, 857142857142857142 (list; graph; refs; listen; history; text; internal format)
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/10) - floor(10^n/21) + floor(10^n/210).

Conjectures from Colin Barker, Nov 06 2017: (Start)

G.f.: x^2*(86 + 83*x + 84*x^2 + 89*x^3 + 81*x^4 + 90*x^5) / ((1 + x)*(1 - 10*x)*(1 - x + x^2)*(1 + x + x^2)).

a(n) = 9*a(n-1) + 9*a(n-2) + 9*a(n-3) + 9*a(n-4) + 9*a(n-5) + 10*a(n-6) for n>7.

(End)

MAPLE

f := n->10^n-floor(10^n/10)-floor(10^n/21)+floor(10^n/210);

PROG

(MAGMA) [10^n-Floor(10^n/10)-Floor(10^n/21)+Floor(10^n/210): n in [2..20]]; // Vincenzo Librandi, Oct 02 2011

CROSSREFS

Cf. A092695.

Sequence in context: A272379 A262916 A262331 * A258584 A034277 A254702

Adjacent sequences:  A128954 A128955 A128956 * A128958 A128959 A128960

KEYWORD

nonn

AUTHOR

Milan Janjic, Apr 28 2007

STATUS

approved

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Last modified January 21 10:05 EST 2022. Contains 350476 sequences. (Running on oeis4.)