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%I #2 Mar 30 2012 17:26:31
%S 0,3,4,3,6,5,8,7,8,9,12,11,14,13,14,15,18,17,20,19,20,21,24,23,24,25,
%T 26,27,30,29,32,31,32,33,34,35,38,37,38,39,42,41,44,43,44,45,48,47,48,
%U 49,50,51,54,53,54,55,56,57,60,59,62,61,62,63,64,65,68,67,68,69,72,71,74
%N a(n)=n+1 if n is prime, otherwise a(n)=n-1.
%t Table[If[PrimeQ[n],n+1,n-1],{n,1,200}]
%Y Cf. A068519, A167480, A167482, A175027.
%K nonn
%O 1,2
%A _Zak Seidov_, Nov 04 2009