OFFSET
1,1
COMMENTS
Necessarily n = 0 (mod 3) because: (a) if n = 3k+1 then 2*n^2 + 25 = 2*(3k+1)^2 + 25 = 2*(9*k^2 + 6*k + 1) + 25 = 18*k^2 + 12*k + 27 = 0 mod 3; (b) if n = 3k-1 then 2*n^2 + 25 = 2*(3k-1)^2 + 25 = 2*(9*k^2 - 6*k + 1) + 25 = 18*k^2 - 12*k + 27 = 0 mod 3; (c) while n = 3k then 2*n^2 + 25 = 2*(3k)^2 + 25 = 18*k^2 + 25 = 1 mod 3, which can be prime. - Jonathan Vos Post, Oct 06 2005
EXAMPLE
If n=96 then (2*n^2) + 25 = 18457 (prime).
PROG
(Magma) [n: n in [0..600] | IsPrime(2*n^2+25)]; // Vincenzo Librandi, Nov 13 2010
(PARI) is(n)=isprime(2*n^2+25) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,easy,changed
AUTHOR
Parthasarathy Nambi, Oct 05 2005
EXTENSIONS
More terms from Jonathan Vos Post, Oct 06 2005
STATUS
approved