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a(n)= primepi(n) if n is prime, otherwise a(n)=prime(n).
4

%I #4 Jul 16 2015 22:00:15

%S 2,1,2,7,3,13,4,19,23,29,5,37,6,43,47,53,7,61,8,71,73,79,9,89,97,101,

%T 103,107,10,113,11,131,137,139,149,151,12,163,167,173,13,181,14,193,

%U 197,199,15,223,227,229,233,239,16,251,257,263,269,271,17,281,18,293,307

%N a(n)= primepi(n) if n is prime, otherwise a(n)=prime(n).

%t Table[If[PrimeQ[n],PrimePi[n],Prime[n]],{n,1,200}]

%Y Cf. A068519 a(n)=n if n is prime otherwise a(n)=prime(n), A175027 a(n)=n if n is nonprime otherwise a(n)=primepi(n).

%K nonn

%O 1,1

%A _Zak Seidov_, Nov 04 2009