|
%I #23 Jul 11 2017 04:51:34
%S 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,
%T 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,
%U 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
%N a(n) = number of primes <= n that end in 9.
%C Partial sums of A185709.
%H G. C. Greubel, <a href="/A185715/b185715.txt">Table of n, a(n) for n = 1..5000</a>
%H A. Granville and G. Martin, <a href="http://www.arXiv.org/abs/math.NT/0408319">Prime number races</a>, arXiv:math/0408319 [math.NT], 2004.
%H A. Granville and G. Martin, <a href="http://www.jstor.org/stable/27641834">Prime number races</a>, Amer. Math. Monthly, 113 (No. 1, 2006), 1-33.
%t Accumulate[Table[If[PrimeQ[n] && Mod[n, 10] == 9, 1, 0], {n, 50}]] (* _G. C. Greubel_, Jul 10 2017 *)
%o (PARI) a(n) = sum(k=1, n, if ((k % 10)==9, isprime(k))); \\ _Michel Marcus_, Jul 11 2017
%Y Cf. A185705, A185706, A185708, A185709, A185711, A185712, A185714, A185715.
%K base,nonn
%O 1,29
%A _N. J. A. Sloane_, Feb 10 2011
|
