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 A070374 a(n) = 5^n mod 21. 1
 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16, 17, 1, 5, 4, 20, 16 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (1,0,-1,1). FORMULA a(n) = (1/30)*{101*(n mod 6)+16*[(n+1) mod 6]+41*[(n+2) mod 6]-59*[(n+3) mod 6]+26*[(n+4) mod 6]+[(n+5) mod 6]}, with n>=0. - Paolo P. Lava, Feb 24 2010 From R. J. Mathar, Apr 20 2010: (Start) a(n) = a(n-1) - a(n-3) + a(n-4). G.f.: ( -1-4*x+x^2-17*x^3 ) / ( (x-1)*(1+x)*(x^2-x+1) ). (End) From G. C. Greubel, Mar 13 2016: (Start) a(n) = a(n-6). E.g.f.: 7*cosh(x) + 14*sinh(x) - 6*exp(x/2)*cos(sqrt(3)*x/2) - 4*sqrt(3)*exp(x/2)*sin(sqrt(3)*x/2). (End) MATHEMATICA PowerMod[5, Range[0, 50], 21] (* G. C. Greubel, Mar 13 2016 *) PROG (Sage) [power_mod(5, n, 21) for n in xrange(0, 83)] # Zerinvary Lajos, Nov 26 2009 (PARI) a(n)=lift(Mod(5, 21)^n) \\ Charles R Greathouse IV, Mar 22 2016 CROSSREFS Sequence in context: A271409 A246326 A272506 * A057423 A215139 A240987 Adjacent sequences:  A070371 A070372 A070373 * A070375 A070376 A070377 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, May 12 2002 STATUS approved

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