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A091189
Primes of the form 20*R_k + 1, where R_k is the repunit (A002275) of length k.
2
2221, 222222222222222221, 2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222221
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).
CROSSREFS
Cf. A056660 (corresponding k), A084832.
Sequence in context: A210712 A260175 A166580 * A046443 A257826 A043500
KEYWORD
bref,nonn
AUTHOR
Rick L. Shepherd, Feb 22 2004
STATUS
approved