G.f. is ((1-x)/(1-2*x)) * G(x*(1-x)/(1-2*x)) where G(x) is g.f. for Catalan numbers A000108.

A059279

G.f. is ((1-x)/(1-2*x)) * G(x*(1-x)/(1-2*x)) where G(x) is g.f. for Catalan numbers A000108.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =20a(4) =72a(5) =276a(6) =1112a(7) =4656a(8) =20080a(9) =88608a(10) =398144a(11) =1815248a(12) =8375904a(13) =39037120a(14) =183493440a(15) =868853120a(16) =4140414720a(17) =19841656960a(18) =95559048960a(19) =462268075520

External references