OFFSET
1,1
COMMENTS
Or: primes of the form k*(k+1)*(k+2)/(k+(k+1)+(k+2))-2.
Generated by k=3, 7, 9, 15, 19, 25, 33, 37, 43, ....
Primes p such that 3*p+7 is a square. - Vincenzo Librandi, Dec 05 2015
Primes of the forms 3*k^2 + 2*k - 2 and 3*k^2 + 4*k - 1. - Robert Israel, Nov 27 2017
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
k=3 contributes a term because 3*(3+2)/3 - 2 = 3 = a(1) is prime.
MAPLE
select(isprime, [seq(seq((3*j+i)*(3*j+i+2)/3-2, i=0..1), j=1..1000)]); # Robert Israel, Nov 27 2017
MATHEMATICA
f[n_]:=(n*(n+1)*(n+2))/(n+(n+1)+(n+2))-2; lst={}; Do[p=f[n]; If[PrimeQ[p], AppendTo[lst, p]], {n, 6!}]; lst
Select[Table[(k(k+2))/3-2, {k, 350}], PrimeQ] (* Harvey P. Dale, May 10 2014 *)
PROG
(Magma) [p: p in PrimesUpTo(45000) | IsSquare(3*p+7)]; // Vincenzo Librandi, Dec 05 2015
(PARI) forprime(p=2, 1e5, if(issquare(3*p+7), print1(p , ", "))) \\ Altug Alkan, Dec 05 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jun 30 2009
EXTENSIONS
Definition simplified by R. J. Mathar, Jul 02 2009
STATUS
approved