The number of boundary edges for all ordered trees with n edges.

Terms

a(0) =1a(1) =4a(2) =14a(3) =47a(4) =157a(5) =529a(6) =1805a(7) =6238a(8) =21812a(9) =77062a(10) =274738a(11) =987276a(12) =3572568a(13) =13007398a(14) =47617798a(15) =175171543a(16) =647227453a(17) =2400843823a(18) =8937670603a(19) =33380986153a(20) =125045165773a(21) =469700405533