OFFSET
0,2
FORMULA
G.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*(-3*n+1)*a(n-1) +(-3*n+11)*a(n-2) +16*(n-3)*a(n-3) +8*(-n+4)*a(n-4)=0. - R. J. Mathar, Feb 29 2016
a(n) = Sum_{k=0..n}((C(k)*Sum_{l=0..n-k}(binomial(k+1,l)*2^l*binomial(n-2*l,n-l-k)))), where C(k) is a Catalan number (A000108). - Vladimir Kruchinin, Mar 15 2016
EXAMPLE
a(2)=2*1*4+1+9. a(3)=2*1*9+4^2+1=35.
MAPLE
l:=1: : k := 0 : m:=4: d(0):=1:d(1):=m: for n from 1 to 28 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, 31); seq(d(n), n=0..29) ;
PROG
(Maxima)
a(n):=sum((binomial(2*k, k)/(k+1)*sum(binomial(k+1, l)*2^l*binomial(n-2*l, n-l-k), l, 0, n-k)), k, 0, n); /* Vladimir Kruchinin, Mar 15 2016 */
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Richard Choulet, Apr 21 2010
STATUS
approved