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A070406
a(n) = 7^n mod 15.
1
1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1, 7, 4, 13, 1
OFFSET
0,2
FORMULA
From R. J. Mathar, Apr 20 2010: (Start)
a(n) = a(n-4).
G.f.: ( -1 - 7*x - 4*x^2 - 13*x^3 ) / ( (x-1)*(1+x)*(1+x^2) ). (End)
E.g.f.: (1/2)*(5*cosh(x) + 20*sinh(x) - 3*cos(x) - 6*sin(x)). - G. C. Greubel, Mar 20 2016
MATHEMATICA
PowerMod[7, Range[0, 50], 15] (* G. C. Greubel, Mar 20 2016 *)
LinearRecurrence[{0, 0, 0, 1}, {1, 7, 4, 13}, 100] (* or *) PadRight[{}, 100, {1, 7, 4, 13}] (* Harvey P. Dale, Oct 13 2018 *)
PROG
(Sage) [power_mod(7, n, 15) for n in range(0, 93)] # Zerinvary Lajos, Nov 27 2009
(PARI) a(n) = lift(Mod(7, 15)^n); \\ Altug Alkan, Mar 20 2016
(Magma) [Modexp(7, n, 15): n in [0..100]]; // Bruno Berselli, Mar 22 2016
CROSSREFS
Sequence in context: A359014 A138339 A107827 * A323997 A297938 A298549
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, May 12 2002
STATUS
approved