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 A073507 Number of primes == 7 (mod 10) less than 10^n. 4
 1, 6, 46, 308, 2411, 19621, 166211, 1440495, 12712314, 113764039, 1029518337, 9401997000, 86516367790 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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 FORMULA A073505(n) + A073506(n) + a(n) + A073508(n) + 2 = A006880(n). EXAMPLE a(2)=6 because there are 6 primes == 7 (mod 10) less than 10^2. They are 7, 17, 37, 47, 67 and 97. MATHEMATICA c = 0; k = 7; Do[While[k < 10^n, If[PrimeQ[k], c++ ]; k += 10]; Print[c], {n, 1, 10}] CROSSREFS Cf. A006880, A087632, A073505, A073506, A073508, A073509, A073510, A073511, A073512, A073513, A073514, A073515, A073516, A073517. Sequence in context: A103768 A325947 A240779 * A155598 A190005 A334609 Adjacent sequences:  A073504 A073505 A073506 * A073508 A073509 A073510 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 May 17 18:55 EDT 2021. Contains 343987 sequences. (Running on oeis4.)