A185715 a(n) = number of primes <= n that end in 9.

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6

Offset: 1

Author

N. J. A. Sloane, Feb 10 2011

Keywords

• base
• nonn

Comments

Partial sums of A185709.

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000
• A. Granville and G. Martin, Prime number races, arXiv:math/0408319 [math.NT], 2004.
• A. Granville and G. Martin, Prime number races, Amer. Math. Monthly, 113 (No. 1, 2006), 1-33.

Crossrefs

Cf. A185705, A185706, A185708, A185709, A185711, A185712, A185714, A185715.

Programs

Mathematica

Accumulate[Table[If[PrimeQ[n] && Mod[n, 10] == 9, 1, 0], {n, 50}]] (* G. C. Greubel, Jul 10 2017 *)

PARI

a(n) = sum(k=1, n, if ((k % 10)==9, isprime(k))); \\ Michel Marcus, Jul 11 2017