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

1,1

Links

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

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 *)

Crossrefs

Sequence in context: A208272 A306086 A045708 * A106102 A053232 A065987

Adjacent sequences: A090147 A090148 A090149 * A090151 A090152 A090153

Keyword

nonn,base

Author

Robert G. Wilson v, Nov 22 2003

Status

approved