A168535 Primes in A028359.

2, 1212121, 12121212121, 1212121212121212121212121212121212121212121

Offset

1,1

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

Links

Table of n, a(n) for n=1..4.

Mathematica

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

Crossrefs

Cf. A028359.

Sequence in context: A324439 A218169 A380589 * A303433 A253264 A375866

Adjacent sequences: A168532 A168533 A168534 * A168536 A168537 A168538

Keyword

nonn

Author

Zak Seidov, Nov 28 2009

Status

approved