A090151 Primes of the form identical digits preceded by a 3.

3, 31, 37, 311, 311111, 31111111111, 311111111111, 377777777777, 31111111111111, 377777777777777777, 31111111111111111111111111111111111, 311111111111111111111111111111111111111111111111

Offset: 1

Author

Robert G. Wilson v, Nov 22 2003

Keywords

• nonn
• base

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..18

Programs

Mathematica

Select[ FromDigits /@ Flatten[ Table[ PadRight[{3}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 24}], 1], PrimeQ[ # ] &]
Select[Union[Flatten[Table[FromDigits[PadRight[{3},n,c]],{n,1000},{c,{1,7}}]]],PrimeQ] (* Harvey P. Dale, Oct 03 2022 *)

Python

from sympy import isprime
def afind(terms):
  print(3, end=", ")
  digits, n = 1, 1
  while n < terms:
    for id in "17":
      t = int('3' + id*digits)
      if isprime(t): print(t, end=", "); n += 1
    digits += 1
afind(12) # Michael S. Branicky, Mar 31 2021