%I
%S 5,17,19,41,43,71,1511,2339,3469,4787,7211,9781
%N Numbers n such that Lucas(4n)/7 is prime.
%C L(k) = Lucas(k) = Fibonacci(k1) + Fibonacci(k+1). 7 = L(4) divides L(4(1+2k)) since L(4n) = L(4)*L(4(n1))  L(4(n2)).
%C Integer n is in this sequence iff n is prime and 4n belongs to A085726. [From _Max Alekseyev_, May 16 2010]
%t a=7; b=47; Do[ c=7ba; a=b; b=c; If[ PrimeQ[c/7], Print[n] ], {n, 3, 100}]
%Y Cf. A000032, A001606 = Indices of prime Lucas numbers. Cf. A074304 = numbers n such that Lucas(2n)/3 is prime.
%K less,more,nonn
%O 1,1
%A _Alexander Adamchuk_, May 14 2007, May 16 2007
%E a(7)  a(10) from _Stefan Steinerberger_, May 17 2007
%E a(11) from _Max Alekseyev_, Nov 25 2007
%E a(12) from _Alexander Adamchuk_, May 15 2010
