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 A073506 Number of primes == 3 (mod 10) less than 10^n. 4
 1, 7, 42, 310, 2402, 19665, 166230, 1440474, 12712499, 113765625, 1029509448, 9401979904, 86516427946 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also Pi(n,5,3) 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. LINKS Eric Weisstein's World of Mathematics, Modular Prime Counting Function FORMULA A073505(n) + a(n) + A073507(n) + A073508(n) + 2 = A006880(n). EXAMPLE 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. MATHEMATICA c = 0; k = 3; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}] CROSSREFS Cf. A006880, A087631, A073505, A073507, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517. Sequence in context: A187246 A278152 A271427 * A025593 A218124 A048862 Adjacent sequences:  A073503 A073504 A073505 * A073507 A073508 A073509 KEYWORD base,nonn,more AUTHOR Shyam Sunder Gupta, Aug 14 2002 EXTENSIONS Edited by Robert G. Wilson v, Oct 03 2002 a(10) from Robert G. Wilson v, Dec 22 2003 a(11)-a(13) from Giovanni Resta, Aug 07 2018 STATUS approved

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Last modified February 24 09:40 EST 2020. Contains 332209 sequences. (Running on oeis4.)