OFFSET
0,3
COMMENTS
((-1)^(n+1))*a(n) = S_{-19}(n), n>=0, defined in A092184.
LINKS
FORMULA
a(n)= 2*(T(n, 21/2)-(-1)^n)/23, with twice Chebyshev's polynomials of the first kind evaluated at x=21/2: 2*T(n, 21/2)=A090729(n)= ((21+sqrt(437))^n + (21-sqrt(437))^n)/2^n.
a(n)= 21*a(n-1)-a(n-2)+2*(-1)^(n+1), n>=2, a(0)=0, a(1)=1.
a(n)= 20*a(n-1) + 20*a(n-2) - a(n-3), n>=3, a(0)=0, a(1)=1, a(2)=19.
G.f.: x*(1-x)/((1+x)*(1-21*x+x^2)) = x*(1-x)/(1-20*x-20*x^2+x^3) (from the Stephan link, see A092184).
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Oct 18 2004
STATUS
approved