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%I #3 Mar 30 2012 18:52:39
%S 1,2,3,4,5,7,12,13,19,31,32,36,37,42,47,53,54,55,58,60,63,78,79,82,83,
%T 91,94,102,105,106,118,125,126,133,135,144,155,156,159,161,163,178,
%U 184,190,206,210,214,216,219,247,248,284,286,288,307,313,315,322
%N Numbers n for which (prime(n) - 1)^2 +1 is prime.
%e a(1) = 1 because (1st prime -1)^2 +1 = (2-1)^2 +1 = 2, a prime; a(2) = 2 because (2nd prime -1)^2 +1 = (3-1)^2 +1 = 5, a prime; a(3) = 3 because (3rd prime -1)^2 +1 = (5-1)^2 +1 = 17, a prime; ... ; a(6) # 6 since (6th prime -1)^2 = (13-1)^2 +1 = 145 = 5*29, which is not a prime; etc.
%t fQ[n_] := PrimeQ[ (Prime@n - 1)^2 + 1]; Select[ Range@ 335, fQ@# &]
%Y Cf. A000040, A006093, A005722 & A127435.
%K nonn
%O 1,2
%A _Juri-Stepan Gerasimov_, Mar 10 2010
%E Edited, corrected and extended by _Robert G. Wilson v_, Mar 14 2010
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