OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 4 followed by the digits 29 is prime (see Example section).
a(21) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 54w29.
EXAMPLE
5 is in this sequence because (49*10^5 - 139)/9 = 544429 is prime.
Initial terms and associated primes:
a(1) = 5, 544429;
a(2) = 6, 5444429;
a(3) = 18, 5444444444444444429;
a(4) = 27, 5444444444444444444444444429; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(49*10^# - 139)/9] &]
PROG
(PARI) isok(k) = isprime((49*10^k - 139)/9); \\ Michel Marcus, Dec 01 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 30 2017
EXTENSIONS
a(19)-a(20) from Robert Price, Mar 04 2019
STATUS
approved