OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 88 followed by k-1 occurrences of the digit 3 followed by the digit 1 is prime (see Example section).
a(28) > 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 883w1.
EXAMPLE
4 is in this sequence because (265*10^4 - 7)/3 = 883331 is prime.
Initial terms and associated primes:
a(1) = 1, 881;
a(2) = 2, 8831;
a(3) = 4, 883331l
a(4) = 9, 88333333331;
a(5) = 13, 883333333333331, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(265*10^# - 7)/3] &]
PROG
(PARI) is(n)=ispseudoprime((265*10^n-7)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jul 10 2016
STATUS
approved