Number of n-node rooted identity trees with thinning limbs and root outdegree (branching factor) 4.

Terms

a(0) =2a(1) =3a(2) =9a(3) =20a(4) =46a(5) =94a(6) =202a(7) =412a(8) =850a(9) =1719a(10) =3483a(11) =6987a(12) =14026a(13) =27990a(14) =55830a(15) =111022a(16) =220589a(17) =437451a(18) =866898a(19) =1715821a(20) =3393973a(21) =6708016a(22) =13251455a(23) =26163174a(24) =51635765a(25) =101868226a(26) =200908954a(27) =396129137a(28) =780868821a(29) =1538971204