%I #15 Jun 13 2017 13:46:52
%S 0,1,2,3,6,7,10,11,17,38,65,133,150,502,537,894,6442,16474,23642,
%T 40894,94133,101335,135737,224437,254621,266782
%N Numbers n such that 4*7^n + 1 is prime.
%t Select[Range[0,2000], PrimeQ[4*7^#+1]&]
%o (PARI) is(n)=ispseudoprime(4*7^n+1) \\ _Charles R Greathouse IV_, Jun 13 2017
%K nonn
%O 1,3
%A _José María Grau Ribas_, Jan 14 2012
%E a(17)-a(26) from _Predrag Kurtovic_, May 24 2015