A090155 Primes of the form identical digits preceded by a 7.

7, 71, 73, 79, 733, 7333, 79999, 733333, 799999, 71111111, 799999999, 79999999999, 79999999999999999999999999, 79999999999999999999999999999999999999999999999999

Offset: 1

Author

Robert G. Wilson v, Nov 22 2003

Keywords

• nonn
• base

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..24

Crossrefs

Subsequence of A030096 and of A030291. Apart from the first term, a subsequence of A235154.

Programs

Mathematica

Select[ FromDigits /@ Flatten[ Table[ PadRight[{7}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 50}], 1], PrimeQ[ # ] &]
Select[FromDigits/@Flatten[Table[PadRight[{7},i,#]&/@{1,3,7,9},{i,50}],1],PrimeQ[#]&]//Union (* Harvey P. Dale, Nov 22 2024 *)