A108966 - OEIS

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A108966

Numbers n such that repunit(n) concatenated with its 10's complement is prime; or numbers n such that (1+7*10^n+100^n)/9 is prime.

%I #3 Dec 15 2017 17:36:51

%S 1,5,16,36,61,149,725,1104,1276,1289,8575

%N Numbers n such that repunit(n) concatenated with its 10's complement is prime; or numbers n such that (1+7*10^n+100^n)/9 is prime.

%C Larger values are only Fermat and Lucas PRPs.

%e a(2)=5 because 10^5-11111 = 88889 and 1111188889 is prime.

%Y Cf. A002275.

%K base,hard,more,nonn

%O 1,2

%A _Jason Earls_, Jul 26 2005