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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Larger values are only Fermat and Lucas PRPs.

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

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

CROSSREFS

Cf. A002275.

Sequence in context: A190970 A077415 A234362 * A321019 A184635 A328506

Adjacent sequences: A108963 A108964 A108965 * A108967 A108968 A108969

KEYWORD

base,hard,more,nonn

AUTHOR

Jason Earls, Jul 26 2005

STATUS

approved

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Last modified December 6 21:00 EST 2022. Contains 358648 sequences. (Running on oeis4.)