OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 6 followed by the digits 97 is prime (see Example section).
a(34) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 76w97.
EXAMPLE
4 is in this sequence because (23*10^4 + 91)/3 = 76697 is prime.
Initial terms and associated primes:
a(1) = 1, 107;
a(2) = 2, 797;
a(3) = 4, 76697;
a(4) = 15, 7666666666666697;
a(5) = 16, 76666666666666697, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(23*10^# + 91)/3] &]
PROG
(PARI) is(n)=ispseudoprime((23*10^n + 91)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 11 2016
EXTENSIONS
a(31) from Robert Price, Aug 11 2019
a(32)-a(33) from Robert Price, May 31 2023
STATUS
approved