G.f. A(x) satisfies: A(x)^2 = A( x^2/(1-4*x) ), with A(0) = 0.

Terms

a(0) =1a(1) =2a(2) =7a(3) =26a(4) =103a(5) =422a(6) =1774a(7) =7604a(8) =33109a(9) =146042a(10) =651256a(11) =2931392a(12) =13301038a(13) =60775340a(14) =279393742a(15) =1291311620a(16) =5996491666a(17) =27962898020a(18) =130883946751a(19) =614664907706