A090157 Primes of the form identical digits preceded by a 9.

97, 911, 977, 97777, 911111, 97777777777777777777, 911111111111111111111, 97777777777777777777777777777, 911111111111111111111111111111111111111111

Offset

1,1

Comments

The identical digits must be either 1 or 7. - Harvey P. Dale, Jun 28 2020

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..21

Mathematica

Select[ FromDigits /@ Flatten[ Table[ PadRight[{9}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 50}], 1], PrimeQ[ # ] &]
Select[Union[Flatten[Table[FromDigits[PadRight[{9}, n, d]], {n, 2, 50}, {d, {1, 7}}]]], PrimeQ]  (* Harvey P. Dale, Jun 27 2020 *)

Crossrefs

Cf. A090148, A090149, A090150, A090151, A090152, A090153, A090154, A090155, A090157.

Sequence in context: A321051 A045715 A113891 * A162674 A070845 A262925

Adjacent sequences: A090154 A090155 A090156 * A090158 A090159 A090160

Keyword

nonn,base

Author

Robert G. Wilson v, Nov 22 2003

Status

approved