OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 0 followed by the digits 39 is prime (see Example section).
a(41) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 70w39.
EXAMPLE
3 is in this sequence because 7*10^3 + 39 = 7039 is prime.
Initial terms and associated primes:
a(1) = 1, 109;
a(2) = 2, 739;
a(3) = 3, 7039;
a(4) = 4, 70000039;
a(5) = 12, 7000000000039, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[7*10^# + 39] &]
PROG
(PARI) is(n)=ispseudoprime(7*10^n+39) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jul 15 2016
EXTENSIONS
a(34)-a(40) from Robert Price, Jul 02 2023
STATUS
approved