OFFSET
0,4
FORMULA
G.f.: (1 - sqrt(1 - 4*x*(1 - x)^2)) / (2*x*(1 - x)^2).
G.f.: 1 / (1 - x*(1 - x)^2 / (1 - x*(1 - x)^2 / (1 - x*(1 - x)^2 / (1 - ...)))), a continued fraction.
a(n) = Sum_{k=0..n} (-1)^(n-k) * binomial(2*k,n-k) * A000108(k).
a(-1) = 0, a(0) = 1; a(n) = Sum_{k=0..n-1} (a(k) - a(k-1)) * (a(n-k-1) - a(n-k-2)).
D-finite with recurrence (n+1)*a(n) -5*n*a(n-1) +2*(6*n-7)*a(n-2) +2*(-6*n+11)*a(n-3) +2*(2*n-5)*a(n-4)=0. - R. J. Mathar, Mar 06 2022
MATHEMATICA
nmax = 33; CoefficientList[Series[(1 - Sqrt[1 - 4 x (1 - x)^2])/(2 x (1 - x)^2), {x, 0, nmax}], x]
Table[Sum[(-1)^(n - k) Binomial[2 k, n - k] CatalanNumber[k], {k, 0, n}], {n, 0, 33}]
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Ilya Gutkovskiy, Jul 10 2020
STATUS
approved