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%N n such that 3^(2n-3)+3^(n-1)+1 is prime.
%C n such that A198410(n) is prime.
%t Select[Range, PrimeQ[((3^(#-1) + 1)^3 -1)/3^#]&]
%Y Cf. A198410, A199192.
%A _Michel Lagneau_, Nov 03 2011