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a(n) = number of primes <= n that end in 1.
4

%I #19 Jul 11 2017 04:51:47

%S 0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,

%T 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,

%U 4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6

%N a(n) = number of primes <= n that end in 1.

%C Partial sums of A185705.

%H G. C. Greubel, <a href="/A185711/b185711.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.dms.umontreal.ca/~andrew/PDF/PrimeRace.pdf">Prime number races</a>, Amer. Math. Monthly, 113 (No. 1, 2006), 1-33.

%t Accumulate[Table[If[PrimeQ[n]&&Mod[n,10]==1,1,0],{n,120}]] (* _Harvey P. Dale_, May 30 2016 *)

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

%K base,nonn

%O 1,31

%A _N. J. A. Sloane_, Feb 10 2011