OFFSET
1,1
COMMENTS
Except for a(0), a(n) mod 180 = 41 or 149 since k must be a multiple of 6 without being a multiple of 30 for k^2+5 to be prime.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1800
Eric Weisstein's World of Mathematics, Near-Square Prime
FORMULA
a(n) = 36 * A056906(n) + 5.
EXAMPLE
a(2)=149 since 12^2 + 5 = 149, which is prime.
MATHEMATICA
Select[Table[n^2+5, {n, 0, 7000}], PrimeQ] (* Vincenzo Librandi, Nov 30 2011 *)
PROG
(Magma) [a: n in [0..700] | IsPrime(a) where a is n^2+5]; // Vincenzo Librandi, Nov 30 2011
(PARI) is(n) = ispseudoprime(n) && issquare(n-5) \\ Felix Fröhlich, May 25 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Henry Bottomley, Jul 07 2000
STATUS
approved