OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 2 followed by the digits 97 is prime (see Example section).
a(25) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 32w97.
EXAMPLE
2 is in this sequence because (29*10^2 + 673)/9 = 397 is prime.
Initial terms and associated primes:
a(1) = 1, 107;
a(2) = 2, 397;
a(3) = 4, 32297;
a(4) = 7, 32222297;
a(5) = 14, 322222222222297; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(29*10^# + 673)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 16 2017
EXTENSIONS
a(24) from Robert Price, Dec 07 2018
STATUS
approved