A068687 Primes which are a sandwich of numbers made of only one digit between two 3's.

313, 353, 373, 383, 3222223, 3444443, 322222223, 355555553, 3111111111113, 3444444444443, 3888888888883, 311111111111113, 377777777777773, 3111111111111111111111111111113, 3888888888888888888888888888883

Offset: 1

Author

Amarnath Murthy, Mar 02 2002

Keywords

• base
• nonn

Comments

a(36) has 1065 digits. - Michael S. Branicky, Jan 28 2023

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..35

Crossrefs

Cf. A068685.

Programs

Python

from sympy import isprime
from itertools import count, islice
def agen(): yield from (t for i in count(1) for m in "124578" if isprime(t:=int("3" + m*i + "3")))
print(list(islice(agen(), 20))) # Michael S. Branicky, Jan 28 2023

Extensions

More terms from Sascha Kurz, Mar 17 2002