G.f. A(x) satisfies A(x) = sqrt( (1 + 2*x) * (1 + 2*x*A(x)) ).

Terms

a(0) =1a(1) =2a(2) =2a(3) =2a(4) =0a(5) =0a(6) =-2a(7) =2a(8) =-2a(9) =6a(10) =-10a(11) =14a(12) =-28a(13) =52a(14) =-86a(15) =158a(16) =-296a(17) =528a(18) =-966a(19) =1806a(20) =-3328a(21) =6160a(22) =-11542a(23) =21590a(24) =-40418a(25) =76118a(26) =-143598a(27) =271138a(28) =-513524a(29) =974620