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 A109009 a(n) = gcd(n,5). 7
 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 1, 1, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Table of n, a(n) for n=0..100. Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,1). FORMULA a(n) = 1 + 4*[5|n], where [x|y] = 1 when x divides y, 0 otherwise. a(n) = a(n-5). Multiplicative with a(p^e, 5) = gcd(p^e, 5). - David W. Wilson, Jun 12 2005 From R. J. Mathar, Apr 04 2011: (Start) Dirichlet g.f.: zeta(s)*(1+4/5^s). G.f.: ( -5-x-x^2-x^3-x^4 ) / ( (x-1)*(1+x+x^2+x^3+x^4) ). (End) a(n) = 4*floor(1/2*cos((2*n*Pi)/5)+1/2) + 1. = 4*floor(((n-1) mod 5)/4) + 1. - Gary Detlefs, Dec 28 2011 MATHEMATICA GCD[Range[0, 100], 5] (* or *) PadRight[{}, 120, {5, 1, 1, 1, 1}] (* Harvey P. Dale, Jun 29 2018 *) PROG (PARI) a(n)=gcd(n, 5) \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Cf. A109004. Sequence in context: A161685 A257461 A129398 * A060904 A351084 A135469 Adjacent sequences: A109006 A109007 A109008 * A109010 A109011 A109012 KEYWORD nonn,easy,mult AUTHOR Mitch Harris STATUS approved

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Last modified September 9 10:46 EDT 2024. Contains 375764 sequences. (Running on oeis4.)