A091189 Primes of the form 20*R_k + 1, where R_k is the repunit (A002275) of length k.

2221, 222222222222222221, 2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222221

Offset: 1

Author

Rick L. Shepherd, Feb 22 2004

Keywords

• bref
• nonn

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

• Makoto Kamada, Prime numbers of the form 22...221.
• Index entries for primes involving repunits

Crossrefs

Cf. A056660 (corresponding k), A084832.

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