A070374 a(n) = 5^n mod 21.

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

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

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 range(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 A327317 A215139

Adjacent sequences: A070371 A070372 A070373 * A070375 A070376 A070377

Keyword

nonn,easy

Author

N. J. A. Sloane, May 12 2002

Status

approved