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%I #20 Jan 21 2016 05:28:53
%S 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,
%T 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,
%U 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
%N a(n) = pi(pi(n)), where pi = A000720.
%C a(n) = a(n-1) + 1 if n is in A006450, otherwise a(n) = a(n-1). - _Robert Israel_, Jan 20 2016
%H R. Zumkeller, <a href="/A132090/b132090.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) ~ n/log^2 n. - _Charles R Greathouse IV_, Aug 12 2014
%p map(numtheory:-pi@@2,[$1..100]); # _Robert Israel_, Jan 20 2016
%t PrimePi@ PrimePi@ Range@ 105 (* _Robert G. Wilson v_, Jan 20 2016 *)
%o (PARI) a(n)=primepi(primepi(n)) \\ _Charles R Greathouse IV_, Aug 12 2014
%o (Haskell)
%o a132090 = a000720 . a000720 -- _Reinhard Zumkeller_, Jun 23 2015
%Y Cf. A000720, A006450, A000040, A000720, A137588.
%K nonn
%O 1,5
%A _Jonathan Vos Post_, Sep 03 2007
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