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If n-th prime is 6m-1, then a(n) = 6m+1. If n-th prime is 6m+1, then a(n) = 6m-1.
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%I #13 Dec 17 2017 14:13:57

%S 7,5,13,11,19,17,25,31,29,35,43,41,49,55,61,59,65,73,71,77,85,91,95,

%T 103,101,109,107,115,125,133,139,137,151,149,155,161,169,175,181,179,

%U 193,191,199,197,209,221,229,227,235,241,239,253,259,265,271,269,275,283

%N If n-th prime is 6m-1, then a(n) = 6m+1. If n-th prime is 6m+1, then a(n) = 6m-1.

%H Michael De Vlieger, <a href="/A107323/b107323.txt">Table of n, a(n) for n = 3..10000</a>

%F a(n) = A000040(n) +2*A173950(n). - _R. J. Mathar_, Dec 17 2017

%p a:=proc(n) if ithprime(n) mod 6 = 5 then ithprime(n)+2 elif ithprime(n) mod 6 = 1 then ithprime(n)-2 else 0 fi end: seq(a(n),n=3..68); # _Emeric Deutsch_, Jun 19 2005

%t Map[If[Mod[#, 6] == 5, # + 2, # - 2] &, Prime@ Range[3, 60]] (* _Michael De Vlieger_, Sep 04 2017 *)

%K nonn

%O 3,1

%A _Leroy Quet_, May 21 2005

%E More terms from _Emeric Deutsch_, Jun 19 2005