OFFSET
1,1
COMMENTS
Clockwise sectors around outside of London Fives dartboard.
LINKS
Wikipedia, Darts
Index entries for linear recurrences with constant coefficients, signature (0,0,0,1).
FORMULA
From Bruno Berselli, Dec 16 2013: (Start)
G.f.: 5*x*(4 + x + 3*x^2 + 2*x^3)/((1 - x)*(1 + x)*(1 + x^2)).
a(n) = 5*(I^(n*(n-1)) - 2*(-1)^n + 5)/2. (End)
From Wesley Ivan Hurt, Jul 07 2016: (Start)
a(n) = 5*(5 + cos(n*Pi/2) - 2*cos(n*Pi) + sin(n*Pi/2) - 2*I*sin(n*Pi))/2.
a(n) = a(n-4) for n>4. (End)
MAPLE
seq(op([20, 5, 15, 10]), n=0..50); # Wesley Ivan Hurt, Jul 07 2016
MATHEMATICA
Flatten[Table[{20, 5, 15, 10}, {17}]]
PROG
(Magma) &cat[[20, 5, 15, 10]: n in [1..17]]; // Bruno Berselli, Dec 16 2013
(PARI) a(n)=[10, 20, 5, 15][n%4+1] \\ Charles R Greathouse IV, Aug 20 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Arkadiusz Wesolowski, Dec 16 2013
STATUS
approved