OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
FORMULA
G.f.: C((x^2+x)/(1-x))*((x^2-2*x-1)/(x^2-1)*(1+x)/(1-x)), where C(x) is g.f. of Catalan numbers (A000108).
a(n) ~ sqrt(55473 + 4469*sqrt(41)) * (5 + sqrt(41))^n / (sqrt(Pi) * n^(3/2) * 2^(n+7)). - Vaclav Kotesovec, Mar 21 2016
Conjecture: (n+1)*a(n) -4* n*a(n-1) +(-13*n+33)*a(n-2) +2*(8*n-17)*a(n-3) +(19*n-69)*a(n-4) +4*(-4*n+15)*a(n-5) +7*(-n+5)*a(n-6) +2*(2*n-13)*a(n-7)=0. - R. J. Mathar, Jun 07 2016
Conjecture: (n+1)*(n^2-5*n+3)*a(n) -2*n*(3*n^2-16*n+14)*a(n-1) +2*(n+4)*(n-3)*a(n-2) +2*(5*n^3-31*n^2+39*n+9)*a(n-3) +(-n^3+2*n^2+21)*a(n-4) -2*(2*n-9)*(n^2-3*n-1)*a(n-5)=0. - R. J. Mathar, Jun 07 2016
MAPLE
A270661 := proc(n)
local a, k ;
a := 0 ;
for k from 0 to n do
a := a+binomial(2*k, k)/(k+1)^2*add(binomial(k+1, n-k-i)*binomial(k+i, k), i=0..n-k) ;
end do:
%*(n+1) ;
end proc: # R. J. Mathar, Jun 07 2016
MATHEMATICA
Table[Sum[(Binomial[2 k, k] Sum[Binomial[k + 1, n - k - i] Binomial[k + i, k], {i, 0, n - k}]/(k + 1)^2) (n + 1), {k, 0, n}], {n, 0, 23}] (* Michael De Vlieger, Mar 21 2016 *)
PROG
(Maxima)
C(x):=(1-sqrt(1-4*x))/(2*x);
makelist(coeff(taylor(C((x^2+x)/(1-x))/x*((x^2-2*x-1)/(x^2-1)*(1+x)/(1-x)), x, 0, 10)*x, x, n), n, 0, 10);
a(n):=(sum((binomial(2*k, k)*sum(binomial(k+1, n-k-i)*binomial(k+i, k), i, 0, n-k))/(k+1)^2, k, 0, n))*(n+1);
(PARI) a(n) = sum(k=0, n, (binomial(2*k, k)*sum(i=0, n-k, (binomial(k+1, n-k-i)*binomial(k+i, k)))/(k+1)^2)*(n+1)); \\ Michel Marcus, Mar 21 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, Mar 20 2016
STATUS
approved