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%I #10 Jan 17 2021 11:09:25
%S 0,1,4,9,12,25,132,192,459,10377,45130,63589,83265
%N Numbers n such that 5*7^n + 2 is prime.
%C Values corresponding to 9, 12, 25, 132, 192 and 459 (389 digits) have been certified prime with Primo. There are no other terms <= 4000.
%C No other terms <= 10^5. - _Tyler NeSmith_
%e 7, 37, 12007, 201768037, 69206436007, 6705343098319824504037
%e are 5*7^0 + 2, 5*7^1 + 2, 5*7^4 + 2, 5*7^9 + 2, 5*7^12 + 2, 5*7^25 + 2,
%e respectively. 5*7^132 + 2 has 113 digits.
%o (PARI) for(n=0,4000,if(isprime(5*7^n+2),print1(n,",")))
%K nonn
%O 1,3
%A _Rick L. Shepherd_, Apr 26 2003
%E a(10)-a(13) from _Tyler NeSmith_, Jan 17 2021
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