A068105 Smallest prime starting with n 5s.

2, 5, 557, 5557, 555521, 555557, 55555517, 55555553, 5555555501, 5555555557, 555555555551, 555555555551, 5555555555551, 555555555555529, 555555555555557, 55555555555555519, 555555555555555559, 555555555555555559, 55555555555555555567, 5555555555555555555087

Offset

0,1

Links

Michael S. Branicky, Table of n, a(n) for n = 0..1000

Formula

a(n) <= A065588(n). - Michael S. Branicky, Feb 05 2021

Prog

(Python)
from sympy import isprime
def a(n):
  if n < 2: return list([2, 5])[n]
  n5s, i, pow10 = int('5'*n), 1, 1
  while True:
    i = 1
    while i < pow10:
      t = n5s * pow10 + i
      if isprime(t): return t
      i += 2
    pow10 *= 10
print([a(n) for n in range(20)]) # Michael S. Branicky, Feb 05 2021

Crossrefs

Cf. A065584, A068103, A068104, A065587, A065588.

Sequence in context: A133378 A283561 A037063 * A065588 A208277 A131748

Adjacent sequences: A068102 A068103 A068104 * A068106 A068107 A068108

Keyword

base,easy,nonn

Author

Amarnath Murthy, Feb 20 2002

Extensions

Edited and extended by Robert G. Wilson v, Feb 21 2002

Corrected by Don Reble, Jan 17 2007

Status

approved