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%I #31 Jun 17 2013 13:28:48
%S 4,4,10,40,990,8712,1691820,69466840,6173190532,4139897208540
%N Least number k such that 7^(2^i) + k is prime for i = 0,1,..,n-1.
%e a(5) = 990 because k = 990 is the minimal k such that N = 7^(2^i) + k is prime for i = 0, 1, 2, 3, 4; N = 997, 1039, 3391, 5765791, 33232930570591. But 7^(2^5) + 990 is divisible by 37 and four other primes.
%Y Cf. A129613, A225560 A226281, A226707.
%K nonn,more
%O 1,1
%A _Robin Garcia_, Jun 16 2013
%E a(10) from _Giovanni Resta_, Jun 16 2013