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A091189 Primes of the form 20*R_n + 1, where R_n is the repunit (A002275) of length n. 2
2221, 222222222222222221, 2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222221 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primes of the form 222...221.

The number of 2's in each term is given by the corresponding term of A056660 and so the first term too large to include above is 222...2221 (with 120 2's).

LINKS

Table of n, a(n) for n=1..3.

Makoto Kamada, Prime numbers of the form 22...221.

Index entries for primes involving repunits

CROSSREFS

Cf. A056660 (corresponding n), A084832.

Cf. A051200, A004022, A093176, A093177, A089346.

Sequence in context: A210712 A260175 A166580 * A046443 A257826 A043500

Adjacent sequences:  A091186 A091187 A091188 * A091190 A091191 A091192

KEYWORD

bref,nonn

AUTHOR

Rick L. Shepherd, Feb 22 2004

STATUS

approved

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Last modified September 18 11:42 EDT 2018. Contains 315130 sequences. (Running on oeis4.)