OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 0 followed by the digits 77 is prime (see Example section).
a(27) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 30w77.
EXAMPLE
6 is in this sequence because 3*10^6 + 77 = 3000077 is prime.
Initial terms and associated primes:
a(1) = 1, 107;
a(2) = 6, 3000077;
a(3) = 9, 3000000077;
a(4) = 10, 30000000077;
a(5) = 11, 300000000077; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[3*10^# + 77] &] (* Corrected by Georg Fischer, Jul 22 2019 *)
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 16 2017
EXTENSIONS
a(24)-a(25) from Robert Price, Sep 01 2018
a(26) from Robert Price, Jun 15 2024
STATUS
approved