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A233820 Period 4: repeat [20, 5, 15, 10].

%I A233820 #16 Sep 08 2022 08:46:06
%S A233820 20,5,15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,
%T A233820 5,15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,5,
%U A233820 15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,5,15,10,20,5
%N A233820 Period 4: repeat [20, 5, 15, 10].
%C A233820 Clockwise sectors around outside of London Fives dartboard.
%H A233820 Wikipedia, <a href="http://en.wikipedia.org/wiki/Darts">Darts</a>
%H A233820 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1).
%F A233820 From _Bruno Berselli_, Dec 16 2013: (Start)
%F A233820 G.f.: 5*x*(4 + x + 3*x^2 + 2*x^3)/((1 - x)*(1 + x)*(1 + x^2)).
%F A233820 a(n) = 5*(I^(n*(n-1)) - 2*(-1)^n + 5)/2. (End)
%F A233820 From _Wesley Ivan Hurt_, Jul 07 2016: (Start)
%F A233820 a(n) = 5*(5 + cos(n*Pi/2) - 2*cos(n*Pi) + sin(n*Pi/2) - 2*I*sin(n*Pi))/2.
%F A233820 a(n) = a(n-4) for n>4. (End)
%p A233820 seq(op([20, 5, 15, 10]), n=0..50); # _Wesley Ivan Hurt_, Jul 07 2016
%t A233820 Flatten[Table[{20, 5, 15, 10}, {17}]]
%o A233820 (Magma) &cat[[20,5,15,10]: n in [1..17]]; // _Bruno Berselli_, Dec 16 2013
%o A233820 (PARI) a(n)=[10,20,5,15][n%4+1] \\ _Charles R Greathouse IV_, Aug 20 2015
%Y A233820 Cf. A003833.
%K A233820 nonn,easy
%O A233820 1,1
%A A233820 _Arkadiusz Wesolowski_, Dec 16 2013