OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 83 is prime (see Example section).
a(27) > 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 42w83.
EXAMPLE
3 is in this sequence because (38*10^3 + 547)/9 = 4283 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 3, 4283;
a(3) = 4, 42283;
a(4) = 9, 4222222283;
a(5) = 10, 42222222283, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(38*10^# + 547)/9] &]
PROG
(PARI) isok(n) = isprime((38*10^n + 547)/9); \\ Michel Marcus, Aug 01 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Aug 01 2016
STATUS
approved