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A006879
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Number of primes with n digits.
(Formerly M3577)
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48
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0, 4, 21, 143, 1061, 8363, 68906, 586081, 5096876, 45086079, 404204977, 3663002302, 33489857205, 308457624821, 2858876213963, 26639628671867, 249393770611256, 2344318816620308, 22116397130086627, 209317712988603747, 1986761935284574233, 18906449883457813088, 180340017203297174362
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OFFSET
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0,2
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COMMENTS
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REFERENCES
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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).
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LINKS
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FORMULA
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a(n) = pi(10^n)-pi(10^(n-1)) where pi(10^(-1)) := 0 (cf. A000720 and A006880).
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EXAMPLE
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As 2, 3, 5, and 7 are the only primes less than 10, a(1) = 4.
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MATHEMATICA
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Differences[PrimePi[10^Range[-1, 25]]] (* Paolo Xausa, Apr 16 2024 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,base,hard,changed
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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