A090537 Least n-digit prime using digit 3 once and rest all 1, or 0 if no such prime exists.

3, 13, 113, 0, 11113, 113111, 0, 11111131, 111111113, 0, 11111111113, 111113111111, 0, 31111111111111, 0, 0, 11111111113111111, 111111111111111131, 0, 11111111111111111131, 131111111111111111111, 0, 11111111111111111311111

Offset: 1

Author

Amarnath Murthy, Dec 08 2003

Keywords

• base
• nonn

Crossrefs

Cf. A090535, A090536, A090538.

Without zeros, subsequence of A107689.

Programs

Python

from sympy import isprime
def agen():
  digits = 0
  while True:
    for i in range(digits+1):
      t = int("1"*(digits-i) + "3" + "1"*i)
      if isprime(t): yield t; break
    else: yield 0
    digits += 1
g = agen()
print([next(g) for i in range(23)]) # Michael S. Branicky, Mar 13 2021

Formula

a(3n+1) = 0.

Extensions

More terms from David Wasserman, Jan 03 2006