%I #20 Sep 08 2022 08:45:12
%S 7,2,1,2,1,2,1,14,1,2,1,2,1,2,7,2,1,2,1,2,1,14,1,2,1,2,1,2,7,2,1,2,1,
%T 2,1,14,1,2,1,2,1,2,7,2,1,2,1,2,1,14,1,2,1,2,1,2,7,2,1,2,1,2,1,14,1,2,
%U 1,2,1,2,7,2,1,2,1,2,1,14,1,2,1,2,1,2,7,2,1,2,1,2,1,14,1,2,1,2,1,2,7,2,1
%N Greatest common divisor of n^2 - 7 and n^2 + 7.
%C a(n) is the product of the periodic sequences [1,2]*[7,1,1,1,1,1,1]. - _Gary Detlefs_, Apr 22 2011
%H Vincenzo Librandi, <a href="/A089129/b089129.txt">Table of n, a(n) for n = 0..1000</a>
%F From _Gary Detlefs_, Apr 22 2011: (Start)
%F a(n) = gcd(n+7, 14).
%F a(n) = (6*(1-(n^6 mod 7))+1)*((n mod 2)+1). (End)
%o (PARI) g(n,k) = for(x=0,n,print1(gcd(x^k-7,x^k+7)","))
%o (Magma) [Gcd(n^2+7,n^2-7): n in [0..100] ]; // _Vincenzo Librandi_, Apr 22 2011
%K easy,nonn
%O 0,1
%A _Cino Hilliard_, Dec 05 2003