OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k - 2 occurrences of the digit 8 followed by the digits 71 is prime (see Example section).
a(22) > 2 * 10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 48w71.
EXAMPLE
3 is in this sequence because (44*10^3 - 161)/9 = 4871 is prime.
Initial terms and associated primes:
a(1) = 1, 31;
a(2) = 3, 4871;
a(3) = 4, 48871;
a(4) = 10, 48888888871; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(44*10^# - 161)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 28 2017
STATUS
approved