OFFSET
1,1
COMMENTS
The "not congruent to 1 mod 3" condition is due to the fact that A090537(3*k+1) = 0.
PROG
(Python)
from sympy import isprime
A342221_list = []
for k in range(1, 10**3):
if k % 3 != 1:
m, l = (10**k-1)//9, 2
for i in range(k):
if isprime(m+l):
break
l *= 10
else:
A342221_list.append(k) # Chai Wah Wu, Mar 15 2021
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Michel Marcus, Mar 14 2021
EXTENSIONS
More terms from Chai Wah Wu, Mar 15 2021
STATUS
approved