OFFSET
1,3
COMMENTS
Except for a(1), a(n) is never a multiple of 5.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = sqrt(A056905(n)-5)/6.
EXAMPLE
a(3)=2 since 36*2^2 + 5 = 149, which is prime.
MATHEMATICA
Select[Range[0, 200], PrimeQ[36#^2+5]&] (* Harvey P. Dale, Jul 25 2011 *)
PROG
(Magma) [n: n in [0..200]| IsPrime(36*n^2+5)]; // Vincenzo Librandi, Jul 14 2012
(PARI) is(n)=isprime(36*n^2+5) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Henry Bottomley, Jul 07 2000
EXTENSIONS
Offset corrected by Arkadiusz Wesolowski, Aug 09 2011
STATUS
approved