Number of 3-linear trees on n nodes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =1a(8) =5a(9) =22a(10) =74a(11) =219a(12) =576a(13) =1394a(14) =3150a(15) =6733a(16) =13744a(17) =26969a(18) =51185a(19) =94323a(20) =169453a(21) =297533a(22) =512006a(23) =865050a(24) =1437739a(25) =2353756a(26) =3801041a(27) =6060918a(28) =9552826a(29) =14894428