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A089129
Greatest common divisor of n^2 - 7 and n^2 + 7.
1
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
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 A372907 A191856
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Dec 05 2003
STATUS
approved