OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 77 is prime (see Example section).
a(33) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 50w77.
EXAMPLE
3 is in this sequence because 5*10^3 + 77 = 5077 is prime.
Initial terms and associated primes:
a(1) = 1, 127;
a(2) = 2, 577;
a(3) = 3, 5077;
a(4) = 4, 50077;
a(5) = 6, 5000077, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[5*10^# + 77] &]
PROG
(PARI) is(n)=ispseudoprime(5*10^n + 77) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 23 2016
EXTENSIONS
a(30)-a(32) from Robert Price, Dec 30 2018
STATUS
approved