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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 29 01:30 EST 2020. Contains 332353 sequences. (Running on oeis4.)