login
A125603
Numbers n such that 3n(n-1)/2 + 1 is prime.
3
4, 5, 9, 12, 17, 20, 21, 24, 32, 37, 40, 45, 49, 56, 57, 69, 72, 77, 81, 84, 85, 96, 100, 104, 105, 109, 116, 117, 125, 132, 136, 140, 141, 145, 152, 157, 164, 165, 169, 172, 181, 185, 189, 192, 196, 204, 205, 216, 217, 220, 221, 224, 245, 257, 264, 269, 272, 277
OFFSET
1,1
LINKS
MATHEMATICA
Select[Range[300], PrimeQ[3# (#-1)/2+1]&] (* Harvey P. Dale, Mar 09 2017 *)
PROG
(PARI) isok(n) = isprime(3*n*(n-1)/2 + 1); \\ Michel Marcus, Oct 11 2013
CROSSREFS
Sequence in context: A228914 A200535 A010405 * A239231 A078507 A060199
KEYWORD
nonn
AUTHOR
Zak Seidov, Nov 27 2006
STATUS
approved