OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 0 followed by the digits 41 is prime (see Example section).
a(29) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 20w41.
EXAMPLE
2 is in this sequence because 2*10^2 + 41 = 241 is prime.
Initial terms and associated primes:
a(1) = 0, 43;
a(2) = 1, 61;
a(3) = 2, 24;
a(4) = 5, 200041;
a(5) = 11, 200000000041; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[2*10^# + 41 &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 25 2017
EXTENSIONS
a(27)-a(28) from Robert Price, May 05 2018
STATUS
approved