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 A006879 Number of primes with n digits. (Formerly M3577) 44
 0, 4, 21, 143, 1061, 8363, 68906, 586081, 5096876, 45086079, 404204977, 3663002302, 33489857205, 308457624821, 2858876213963, 26639628671867, 249393770611256, 2344318816620308, 22116397130086627, 209317712988603747, 1986761935284574233, 18906449883457813088, 180340017203297174362 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The number of primes between 10^(n-1) and 10^n. - Cino Hilliard, May 31 2008 [Corrected by Jon E. Schoenfield, Nov 29 2008] REFERENCES J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 21, pp 8, Ellipses, Paris 2008. C. T. Long, Elementary Introduction to Number Theory. Prentice-Hall, Englewood Cliffs, NJ, 1987, p. 77. P. Ribenboim, The Book of Prime Number Records. Springer-Verlag, NY, 2nd ed., 1989, p. 179. D. Shanks, Solved and Unsolved Problems in Number Theory. Chelsea, NY, 2nd edition, 1978, p. 15. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS David Baugh, Table of n, a(n) for n = 0..28(terms 0..24 by Charles R Greathouse IV, a(25) by Vladimir Pletser) C. K. Caldwell, How Many Primes Are There? FORMULA a(n) = pi(10^n)-pi(10^(n-1)) where pi(10^(-1)) := 0 (cf. A000720 and A006880). EXAMPLE As 2, 3, 5, and 7 are the only primes less than 10, a(1) = 4. PROG (PARI) a(n)=primepi(10^n)-primepi(10^(n-1)) \\ Charles R Greathouse IV, May 03 2012 CROSSREFS First differences of A006880. Cf. A309329. Sequence in context: A120368 A053482 A158577 * A228063 A228111 A305986 Adjacent sequences:  A006876 A006877 A006878 * A006880 A006881 A006882 KEYWORD nonn,base,hard AUTHOR EXTENSIONS a(11) and a(12) corrected by Jud McCranie and Enoch Haga a(19) corrected and a(20) added by Paul Zimmermann a(21)-a(22) from Vladeta Jovovic, Nov 07 2001 STATUS approved

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Last modified January 23 17:28 EST 2021. Contains 340385 sequences. (Running on oeis4.)