OFFSET
2,2
FORMULA
a(n)=(n + 2)*(n^2 + 10*n + 15)/30 - 1/5*(1 + ( - 1/2 + 3/10*5^(1/2))*cos(2*n*Pi/5) + (1/5*2^(1/2)*(5 + 5^(1/2))^(1/2) + 1/10*2^(1/2)*(5 - 5^(1/2))^(1/2))*sin(2*n*Pi/5) + ( - 1/2 - 3/10*5^(1/2))*cos(4*n*Pi/5) + ( - 1/10*2^(1/2)*(5 + 5^(1/2))^(1/2) + 1/5*2^(1/2)*(5 - 5^(1/2))^(1/2))*sin(4*n*Pi/5)) [From Richard Choulet, Dec 14 2008]
a(n)= 3*a(n-1) -3*a(n-2) +a(n-3) +a(n-5) -3*a(n-6) +3*a(n-7) -a(n-8). G.f.: -x^2*(-1+x-2*x^2+x^3)/( (x^4+x^3+x^2+x+1) * (x-1)^4 ). [From R. J. Mathar, Oct 05 2009]
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved