A090150 Primes of the form a string of identical digits preceded by a 2.

2, 23, 29, 211, 233, 277, 2111, 2333, 2777, 2999, 23333, 2999999, 29999999, 2777777777, 23333333333, 2111111111111, 2777777777777777, 23333333333333333, 2111111111111111111, 2777777777777777777

Offset: 1

Author

Robert G. Wilson v, Nov 22 2003

Keywords

• nonn
• base

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..47

Programs

Mathematica

Select[ FromDigits /@ Flatten[ Table[ PadRight[{2}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 23}], 1], PrimeQ[ # ] &]
Select[Union[Flatten[Table[FromDigits[PadRight[{2},n,d]],{n,20},{d,{1,3,7,9}}]]],PrimeQ] (* Harvey P. Dale, Aug 25 2016 *)