OFFSET
0,2
FORMULA
G.f: (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=-1, l=-1).
Conjecture: (n+1)*a(n) +(2-7n)*a(n-1) +(11n-13)*a(n-2) + (11n-46)*a(n-3) +4*(29-7n)*a(n-4) +12(n-5)*a(n-5)=0. - R. J. Mathar, Nov 21 2011
EXAMPLE
a(2)=2*1*2-2-1=1. a(3)=2*1*1-2+2^2-1-1=2. a(4)=2*1*2-2+2*2*1-2-1=3.
MAPLE
l:=-1: : k := -1 : 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 29 2010
STATUS
approved