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 67 is prime (see Example section).
a(25) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 30w67.
EXAMPLE
2 is in this sequence because 3*10^2 + 67 = 367 is prime.
Initial terms and associated primes:
a(1) = 1, 97;
a(2) = 2, 367;
a(3) = 3, 3067;
a(4) = 25, 30000000000000000000000067; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[3*10^# + 67] &]
PROG
(PARI) isok(k) = isprime(3*10^k + 67); \\ Michel Marcus, Nov 20 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 19 2017
STATUS
approved