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Numbers n such that 10^n*(7+3*10^n)+3 is prime.
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%I #4 Dec 15 2017 17:37:10

%S 0,1,2,3,7,20,22,65,122,355,561,2216,5638,7271

%N Numbers n such that 10^n*(7+3*10^n)+3 is prime.

%C Values corresponding to n=5638 and n=7271 were both certified Fermat and Lucas PRPs with WinPFGW and submitted to Lifchitz's Top PRPs database.

%o (PARI) is(n)=ispseudoprime(10^n*(7+3*10^n)+3) \\ _Charles R Greathouse IV_, Jun 13 2017

%K more,nonn

%O 1,3

%A _Jason Earls_, Dec 14 2009