Symmetries in planted 4-trees on n+1 vertices.

Terms

a(0) =1a(1) =1a(2) =3a(3) =10a(4) =17a(5) =38a(6) =106a(7) =253a(8) =716a(9) =1903a(10) =5053a(11) =13786a(12) =39293a(13) =107641a(14) =302807a(15) =860099a(16) =2450684a(17) =7038472a(18) =20316895a(19) =58849665a(20) =171217429a(21) =499926666a(22) =1464276207a(23) =4301706250a(24) =12671810107a(25) =37419912977a(26) =110759884262a(27) =328525197554