OFFSET
1,1
COMMENTS
The decimal expansion of 10^k + 1111 consists of a single '1' digit followed by k-4 '0' digits followed by four '1' digits. (See Example section.)
a(18) > 40000. - Michael S. Branicky, Aug 07 2024
EXAMPLE
101111 is prime, so 5 is in the sequence;
100000001111 is prime, so 11 is in the sequence.
PROG
(PARI) isok(n) = (n > 4) && isprime(10^n+1111); \\ Michel Marcus, Oct 15 2013
(Python)
from sympy import isprime, prime
def afind(limit, startk=5):
k, pow10 = startk, 10**startk
for k in range(startk, limit+1):
if isprime(pow10 + 1111): print(k, end=", ")
pow10 *= 10
afind(800) # Michael S. Branicky, Jan 22 2022
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Zak Seidov, Dec 06 2008
EXTENSIONS
Comments and example edited by Jon E. Schoenfield, Jan 14 2015
a(15)-a(17) from Michael S. Branicky, Jan 22 2022
STATUS
approved