OFFSET
1,1
COMMENTS
The sum of the reciprocals converges to 0.350314... Are there infinitely many primes of this form?
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..6800
MATHEMATICA
Intersection[Table[n^2+7, {n, 0, 10^2}], Prime[Range[9*10^3]]] ...or... For[i=7, i<=7, a={}; Do[If[PrimeQ[n^2+i], AppendTo[a, n^2+i]], {n, 0, 100}]; Print["n^2+", i, ", ", a]; i++ ] (* Vladimir Joseph Stephan Orlovsky, Apr 29 2008 *)
Select[Table[n^2+7, {n, 0, 70000}], PrimeQ] (* Vincenzo Librandi, Nov 30 2011 *)
PROG
(PARI) nsqpm(n) = {sr=0; forstep(x=0, n, 2, y = x*x+7; if(isprime(y), print1(y" "); sr+=1.0/y; ); ); print(); print(sr); } \\ Primes of the form n^2 + 7 and the sum of the reciprocals.
(Magma) [a: n in [0..700] | IsPrime(a) where a is n^2+7]; // Vincenzo Librandi, Nov 30 2011
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Dec 26 2002
STATUS
approved