OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..9
Makoto Kamada, Prime numbers of the form 133...33.
MATHEMATICA
Select[Table[FromDigits[PadRight[{1}, n, 3]], {n, 500}], PrimeQ] (* Vincenzo Librandi, Apr 06 2019 *)
PROG
(Magma) [a: n in [0..100] | IsPrime(a) where a is ((4*10^n-1) div 3)]; // Vincenzo Librandi, Apr 06 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Apr 08 2004
STATUS
approved