OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-1 occurrences of the digit 3 followed by the digits 03 is prime (see Example section).
a(31) > 3*10^5.
LINKS
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 53w03.
EXAMPLE
3 is in this sequence because (16*10^3 - 91)/3 = 5303 is prime.
Initial terms and associated primes:
a(1) = 1, 23;
a(2) = 2, 503;
a(3) = 3, 5303;
a(4) = 5, 533303;
a(5) = 16, 53333333333333303, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(16*10^# - 91)/3] &]
PROG
(PARI) is(n)=ispseudoprime((16*10^n - 91)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Jun 22 2016
EXTENSIONS
a(28)-a(30) from Robert Price, Jun 01 2023
STATUS
approved