A093162 Primes of the form 20*R_k + 3, where R_k is the repunit (A002275) of length k.

3, 23, 223, 22222223, 22222222223, 222222222222222222222222222222222223

Offset: 1

Author

Rick L. Shepherd, Mar 26 2004

Keywords

• nonn

Comments

The next term (a(7)) has 95 digits. - Harvey P. Dale, Dec 26 2022

Links

• Makoto Kamada, Prime numbers of the form 22...223.
• Index entries for primes involving repunits

Crossrefs

Cf. A002275, A056656 (corresponding k, and count of digits 2 in a(n)), A096506.

Programs

Mathematica

Select[Table[FromDigits[PadLeft[{3},n,2]],{n,40}],PrimeQ] (* Harvey P. Dale, Dec 26 2022 *)

Formula

a(n) = (20*10^A056656(n) + 7)/9 = (2*10^A096506(n) + 7)/9.

Extensions

Edited by Ray Chandler, Feb 27 2012