%I #4 Jul 16 2015 22:01:45
%S 0,1,1,2,4,3,6,4,8,9,10,5,12,6,14,15,16,7,18,8,20,21,22,9,24,25,26,27,
%T 28,10,30,11,32,33,34,35,36,12,38,39,40,13,42,14,44,45,46,15,48,49,50,
%U 51,52,16,54,55,56,57,58,17,60,18,62,63,64,65,66,19,68,69,70,20,72,21
%N Replace prime with its index!
%F a(n)=n if n is nonprime otherwise a(n)=primepi(n).
%t Table[If[PrimeQ[n],PrimePi[n],n],{n,0,200}]
%Y Cf. A068519.
%K nonn
%O 0,4
%A _Zak Seidov_, Nov 04 2009
