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%I #14 Aug 07 2018 11:17:15
%S 1,7,42,310,2402,19665,166230,1440474,12712499,113765625,1029509448,
%T 9401979904,86516427946
%N Number of primes == 3 (mod 10) less than 10^n.
%C Also Pi(n,5,3)
%C This and the related sequences A073505-A073517 and A006880, A073548-A073565 are included because there is interest in the distribution of primes by their initial or final digits.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ModularPrimeCountingFunction.html">Modular Prime Counting Function</a>
%F A073505(n) + a(n) + A073507(n) + A073508(n) + 2 = A006880(n).
%e a(2)=7 because there are 7 primes == 3 (mod 10) less than 10^2. They are 3, 13, 23, 43, 53, 73 and 83.
%t c = 0; k = 3; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}]
%Y Cf. A006880, A087631, A073505, A073507, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517.
%K base,nonn,more
%O 1,2
%A _Shyam Sunder Gupta_, Aug 14 2002
%E Edited by _Robert G. Wilson v_, Oct 03 2002
%E a(10) from _Robert G. Wilson v_, Dec 22 2003
%E a(11)-a(13) from _Giovanni Resta_, Aug 07 2018