OFFSET
0,2
FORMULA
G.f f: f(z)=(1-sqrt(1-4*z*(a(0)-z*a(0)^2+z*a(1)+(k+l)*z^2/(1-z)+k*z^2/(1-z)^2)))/(2*z) (k=0, l=-1).
Conjecture: (n+1)*a(n) +2(1-3n)*a(n-1) +(19-7n)*a(n-2) +4*(8n-25)*a(n-3) +20(4-n)*a(n-4)=0. - R. J. Mathar, Nov 27 2011
EXAMPLE
a(2)=2*1*5-1=9. a(3)=2*1*9+5^2-1=42. a(4)=2*1*42+2*5*9-1=173.
MAPLE
l:=-1: : k := 0 : m:=2:d(0):=1:d(1):=m: for n from 1 to 30 do d(n+1):=sum(d(p)*d(n-p)+k, p=0..n)+l:od :
taylor((1-sqrt(1-4*z*(d(0)-z*d(0)^2+z*m+(k+l)*z^2/(1-z)+k*z^2/(1-z)^2)))/(2*z), z=0, 30); seq(d(n), n=0..30);
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Richard Choulet, Apr 25 2010
STATUS
approved