OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 61 is prime (see Example section).
a(31) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 43w61.
EXAMPLE
5 is in this sequence because (13*10^5 + 83) / 3 = 433361 is prime.
Initial terms and associated primes:
a(1) = 1, 71;
a(2) = 2, 461;
a(3) = 5, 433361;
a(4) = 7, 43333361;
a(5) = 17, 433333333333333361, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(13*10^# + 83) / 3] &]
PROG
(PARI) is(n)=ispseudoprime((13*10^n + 83)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Sep 01 2016
STATUS
approved