A132090 - OEIS

A132090

a(n) = pi(pi(n)), where pi = A000720.

0, 0, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,5

COMMENTS

a(n) = a(n-1) + 1 if n is in A006450, otherwise a(n) = a(n-1). - Robert Israel, Jan 20 2016

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

a(n) ~ n/log^2 n. - Charles R Greathouse IV, Aug 12 2014

MAPLE

map(numtheory:-pi@@2, [$1..100]); # Robert Israel, Jan 20 2016

MATHEMATICA