OFFSET
1,2
COMMENTS
All terms except the first one are multiples of 3. - Zak Seidov, Feb 24 2006
And because of this, all the primes except for the first one are congruent to 1 (mod 6). - Robert G. Wilson v, Aug 05 2014
For any n in this sequence, 3*(2*n^2 + 1) has the same nonzero digits as its prime factors in base 2n. - Ely Golden, Dec 12 2016
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n)=((A090698(n)-1)/2)^(1/2).
Starting with n=2, a(n)=3*A089008(n-1). - Zak Seidov, Feb 24 2006
MATHEMATICA
Select[Range[500], PrimeQ[2#^2 + 1]&] (* Vincenzo Librandi, Jan 07 2013 *)
PROG
(Magma) [n: n in [1..500] | IsPrime(2*n^2+1)]; // Vincenzo Librandi, Jan 07 2013
(PARI) is(n)=isprime(2*n^2+1) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Dec 20 2003
STATUS
approved