OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..17
Makoto Kamada, Prime numbers of the form 233...33.
FORMULA
Primes of the form 2 * 10^k + 3 * R_k, where R_k is the repunit (A002275) of length k.
MAPLE
select(isprime, [seq(7*10^k-1)/3, k=0..100)]): # Robert Israel, Aug 07 2014
MATHEMATICA
Select[(7 * 10^Range[0, 19] - 1)/3, PrimeQ] (* Alonso del Arte, Aug 07 2014 *)
Select[Table[FromDigits[PadRight[{2}, n, 3]], {n, 100}], PrimeQ] (* Harvey P. Dale, Oct 04 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Apr 08 2004
EXTENSIONS
Simpler definition from Alonso del Arte, Aug 07 2014
One more term (a(10)) from Harvey P. Dale, Oct 04 2015
STATUS
approved