OFFSET
1,3
COMMENTS
For k > 0, numbers k such that the digits 44 followed by k-1 occurrences of the digit 0 followed by the digit 3 is prime (see Example section).
a(29) > 2*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 440w3.
EXAMPLE
1 is in this sequence because 44*10^1 + 3 = 443 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 1, 443;
a(3) = 6, 44000003;
a(4) = 7, 440000003;
a(5) = 27, 44000000000000000000000000003; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[44*10^# + 3] &]
PROG
(PARI) isok(k) = ispseudoprime(44*10^k + 3) \\ Altug Alkan, Aug 27 2017
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Aug 27 2017
EXTENSIONS
a(28) from Robert Price, Apr 09 2020
STATUS
approved