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a(n)=2*n if n is prime, otherwise a(n)=3*n.
1

%I #2 Mar 30 2012 17:26:31

%S 3,4,6,12,10,18,14,24,27,30,22,36,26,42,45,48,34,54,38,60,63,66,46,72,

%T 75,78,81,84,58,90,62,96,99,102,105,108,74,114,117,120,82,126,86,132,

%U 135,138,94,144,147,150,153,156,106,162,165,168,171,174,118,180,122,186

%N a(n)=2*n if n is prime, otherwise a(n)=3*n.

%t Table[If[PrimeQ[n],2*n,3*n],{n,1,200}]

%Y Cf. A068519, A167480, A167482, A175027, A175028.

%K nonn

%O 1,1

%A _Zak Seidov_, Nov 04 2009