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Search: id:A101225
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| A101225 |
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Numbers formed by the third nesting of pi(10^n). |
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+0
3
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| 1, 4, 12, 46, 194, 977, 5492, 33666, 220068, 1513371, 10833076, 80104927, 608455060, 4726881850, 37431015268
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(n) = pi(pi(pi(10^n))) where pi(x) is the number of primes LE x.
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EXAMPLE
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a(3) = pi(pi(pi(10^3))) = 12, the third entry in the table.
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MATHEMATICA
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f[n_] := Nest[PrimePi, 10^n, 3]; Table[ f[n], {n, 13}] (from Robert G. Wilson v Dec 20 2004)
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PROGRAM
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(PARI) nestpi(n, m) = { local(x, y, z); for(x=1, n, z=10^x; for(y=1, m, z=pi(z)); print1(z", ")) } pi(n) = \pi(n) Prime count function { local(c, x); c=0; forprime(x=1, n, c++); return(c) }
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CROSSREFS
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Cf. A006880, A096359.
Sequence in context: A126202 A149373 A151464 this_sequence A000775 A149374 A149375
Adjacent sequences: A101222 A101223 A101224 this_sequence A101226 A101227 A101228
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KEYWORD
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nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Dec 15 2004
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 20 2004
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