A101226 Numbers formed by the fourth nesting of pi(10^n).

0, 2, 5, 14, 44, 165, 725, 3607, 19624, 115127, 716177, 4675144, 31743253

Offset

1,2

Links

Table of n, a(n) for n=1..13.

Formula

a(n) = pi(pi(pi(pi(10^n)))) where pi(x) is the number of primes LE x.

Example

a(3) = pi(pi(pi(pi(10^3)))) = 5, the third entry in the table.

Mathematica

f[n_] := Nest[PrimePi, 10^n, 4]; Table[ f[n], {n, 13}] (* Robert G. Wilson v, Dec 21 2004 *)

Prog

(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) }

Crossrefs

Cf. A006880, A096359, A101225.

Sequence in context: A368636 A060996 A134378 * A240610 A149887 A149888

Adjacent sequences: A101223 A101224 A101225 * A101227 A101228 A101229

Keyword

nonn

Author

Cino Hilliard, Dec 15 2004

Extensions

a(10)-a(14) from Robert G. Wilson v, Dec 21 2004

Status

approved