A089129 Greatest common divisor of n^2 - 7 and n^2 + 7.

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, 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, 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

Offset

0,1

Comments

a(n) is the product of the periodic sequences [1,2]*[7,1,1,1,1,1,1]. - Gary Detlefs, Apr 22 2011

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Formula

From Gary Detlefs, Apr 22 2011: (Start)

a(n) = gcd(n+7, 14).

a(n) = (6*(1-(n^6 mod 7))+1)*((n mod 2)+1). (End)

Prog

(PARI) g(n, k) = for(x=0, n, print1(gcd(x^k-7, x^k+7)", "))
(Magma) [Gcd(n^2+7, n^2-7): n in [0..100] ]; // Vincenzo Librandi, Apr 22 2011

Crossrefs

Sequence in context: A021585 A103713 A197184 * A100957 A191856 A220862

Adjacent sequences: A089126 A089127 A089128 * A089130 A089131 A089132

Keyword

easy,nonn

Author

Cino Hilliard, Dec 05 2003

Status

approved