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A101225
Numbers formed by the third nesting of pi(10^n).
2
1, 4, 12, 46, 194, 977, 5492, 33666, 220068, 1513371, 10833076, 80104927, 608455060, 4726881850, 37431015268, 301327263751, 2460711566651, 20348625806080, 170149286304116, 1436870802519360, 12241980697771924, 105136072207222852, 909475787902559408, 7919305232077304848
OFFSET
1,2
LINKS
Jonathan Bayless, Dominic Klyve, and Tomás Oliveira e Silva, New Bounds and Computations on Prime-Indexed Primes, INTEGERS, Electronic J. of Combinatorial Number Theory, Vol. 13, Paper A43, 2013.
FORMULA
a(n) = pi(pi(pi(10^n))) where pi(x) is the number of primes <= x.
EXAMPLE
a(3) = pi(pi(pi(10^3))) = 12, the third entry in the table.
MATHEMATICA
f[n_] := Nest[PrimePi, 10^n, 3]; Table[ f[n], {n, 13}] (* Robert G. Wilson v, Dec 20 2004 *)
PROG
(PARI) nestpi(n, m) = { local(x, y, z); for(x=1, n, z=10^x; for(y=1, m, z=primepi(z)); print1(z", ")) }
CROSSREFS
Sequence in context: A149373 A259203 A151464 * A000775 A149374 A149375
KEYWORD
nonn
AUTHOR
Cino Hilliard, Dec 15 2004
EXTENSIONS
More terms from Robert G. Wilson v, Dec 20 2004
a(16)-a(24) from Robert G. Wilson v, Mar 11 2015
STATUS
approved