

A091189


Primes of the form 20*R_n + 1, where R_n is the repunit (A002275) of length n.


2




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



