OFFSET
1,2
COMMENTS
a(n) == 4 (mod 6) for n > 1.
1 and numbers k such that (10^k + 3)/7 is prime.
EXAMPLE
4 is a term because ceiling(10^4/7) = 1429 is prime.
.
n | k = a(n) | ceiling(10^k/7)
--+----------+-----------------
1 | 1 | 2
2 | 4 | 1429
3 | 10 | 1428571429
4 | 16 | 1428571428571429
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Jon E. Schoenfield, Jan 27 2024
STATUS
approved