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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.
1
1, 5, 16, 36, 61, 149, 725, 1104, 1276, 1289, 8575
OFFSET
1,2
COMMENTS
Larger values are only Fermat and Lucas PRPs.
EXAMPLE
a(2)=5 because 10^5-11111 = 88889 and 1111188889 is prime.
CROSSREFS
Cf. A002275.
Sequence in context: A234362 A363613 A363605 * A321019 A184635 A328506
KEYWORD
base,hard,more,nonn
AUTHOR
Jason Earls, Jul 26 2005
STATUS
approved