OFFSET
3,2
LINKS
Michael De Vlieger, Table of n, a(n) for n = 3..1792
László Németh and László Szalay, Sequences Involving Square Zig-Zag Shapes, J. Int. Seq., Vol. 24 (2021), Article 21.5.2.
Index entries for linear recurrences with constant coefficients, signature (8,-21,20,-5).
FORMULA
a(n) = (1/5)*Sum_{r=1..9} sin(r*Pi/10)*sin(7*r*Pi/10)*(2*cos(r*Pi/10))^(2n).
a(n) = 8*a(n-1) - 21*a(n-2) + 20*a(n-3) - 5*a(n-4).
G.f.: x^3*(1-x)/( (1-3*x+x^2)*(1-5*x+5*x^2) ).
MATHEMATICA
LinearRecurrence[{8, -21, 20, -5}, {1, 7, 35, 153}, 30] (* Harvey P. Dale, Jan 16 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Herbert Kociemba, Jun 15 2004
STATUS
approved