A168535 Primes in A028359.

2, 1212121, 12121212121, 1212121212121212121212121212121212121212121

Offset: 1

Author

Zak Seidov, Nov 28 2009

Keywords

• nonn

Comments

Except for the first term, each term must both begin and end with a "1" because each term greater than 2 must end in a "1" and if a term begins with a "2" the sum of the digits of the term will be divisible by 3 and thus the term is not a prime. - Harvey P. Dale, Jun 22 2019

The next term (a(5)) has 139 digits and a(6) has 627 digits. - Harvey P. Dale, Jun 22 2019

Crossrefs

Cf. A028359.

Programs

Mathematica

Join[{2},Select[Table[FromDigits[PadRight[{},2n+1,{1,2}]],{n,30}],PrimeQ]] (* Harvey P. Dale, Jun 22 2019 *)