This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A132090 #20 Jan 21 2016 05:28:53 %S A132090 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 A132090 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 A132090 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 A132090 a(n) = pi(pi(n)), where pi = A000720. %C A132090 a(n) = a(n-1) + 1 if n is in A006450, otherwise a(n) = a(n-1). - _Robert Israel_, Jan 20 2016 %H A132090 R. Zumkeller, <a href="/A132090/b132090.txt">Table of n, a(n) for n = 1..10000</a> %F A132090 a(n) ~ n/log^2 n. - _Charles R Greathouse IV_, Aug 12 2014 %p A132090 map(numtheory:-pi@@2,[$1..100]); # _Robert Israel_, Jan 20 2016 %t A132090 PrimePi@ PrimePi@ Range@ 105 (* _Robert G. Wilson v_, Jan 20 2016 *) %o A132090 (PARI) a(n)=primepi(primepi(n)) \\ _Charles R Greathouse IV_, Aug 12 2014 %o A132090 (Haskell) %o A132090 a132090 = a000720 . a000720 -- _Reinhard Zumkeller_, Jun 23 2015 %Y A132090 Cf. A000720, A006450, A000040, A000720, A137588. %K A132090 nonn %O A132090 1,5 %A A132090 _Jonathan Vos Post_, Sep 03 2007