OFFSET
1,3
COMMENTS
For k > 0, numbers k such that the digits 33 followed by k-1 occurrences of the digit 9 followed by the digit 7 is prime (see Example section).
a(26) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 339w7.
EXAMPLE
3 is in this sequence because 34*10^3 - 3 = 33997 is prime.
Initial terms and associated primes:
a(1) = 0, 31;
a(2) = 1, 337;
a(3) = 3, 33997;
a(4) = 5, 3399997;
a(5) = 7, 339999997; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[34*10^# - 3] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 21 2017
STATUS
approved