OFFSET
1,1
COMMENTS
If n == 1 mod 3, then (n - 1)/3 is in A086285.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
(2^2 + 2)/3 = 6/3 = 2, which is prime, so 2 is in the sequence.
(7^2 + 2)/3 = 51/3 = 17, which is prime, so 7 is in the sequence.
(11^2 + 2)/3 = 123/3 = 41, which is prime, so 11 is in the sequence.
(13^2 + 2)/3 = 171/3 = 57 = 3 * 19, which is not prime, so 13 is not in the sequence.
MAPLE
N:= 10000; # to get all terms <= 3 N + 2
A240878:= select(t -> isprime((t^2+2)/3), {seq(seq(3*i+j, j=1..2), i=0..N)}):
MATHEMATICA
Select[Range[500], PrimeQ[(#^2 + 2)/3] &] (* Alonso del Arte, Apr 13 2014 *)
PROG
(Magma) [2] cat [n: n in [4..600] | IsPrime((n^2 + 2) div 3)]; // Vincenzo Librandi, Jul 01 2014
(PARI) is(n)=isprime((n^2+2)/3) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Robert Israel, Apr 13 2014
STATUS
approved