Number of 4-ary plane multitrees with n edges.

Terms

a(0) =1a(1) =1a(2) =3a(3) =10a(4) =36a(5) =121a(6) =447a(7) =1699a(8) =6589a(9) =25914a(10) =103633a(11) =419421a(12) =1714463a(13) =7068285a(14) =29361629a(15) =122764876a(16) =516245009a(17) =2181957489a(18) =9264275600a(19) =39495666700a(20) =169000837410a(21) =725574719515