a(n) = [x^n] S(x)^(2*n), where S(x) = (1 - x - sqrt(1 - 6*x + x^2))/(2*x) is the o.g.f. of the large Schröder numbers A006318.

A333481

a(n) = [x^n] S(x)^(2*n), where S(x) = (1 - x - sqrt(1 - 6*x + x^2))/(2*x) is the o.g.f. of the large Schröder numbers A006318.

Terms

    a(0) =1a(1) =4a(2) =48a(3) =652a(4) =9344a(5) =138004a(6) =2077968a(7) =31712412a(8) =488793088a(9) =7591462564a(10) =118615816048

External references