OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 5 followed by the digits 93 is prime (see Example section).
a(23) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 35w93.
EXAMPLE
3 is in this sequence because (32*10^3 + 337)/9 = 3593 is prime.
Initial terms and associated primes:
a(1) = 0, 41;
a(2) = 1, 73;
a(3) = 3, 3593;
a(4) = 4; 35593; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(32*10^# + 337)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jul 25 2017
STATUS
approved