OFFSET
1,1
COMMENTS
For k > 0, numbers k such that the digits 39 followed by k-1 occurrences of the digit 0 followed by the digit 1 is prime (see Example section).
a(26) > 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 390w1.
EXAMPLE
6 is in this sequence because 39*10^6 + 1 = 39000001 is prime.
Initial terms and associated primes:
a(1) = 4, 390001;
a(2) = 6, 39000001;
a(3) = 12, 39000000000001;
a(4) = 14, 3900000000000001;
a(5) = 18, 39000000000000000001; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[39*10^# + 1] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 10 2017
STATUS
approved