Number of trees with n nodes, 3 of which are labeled.

Terms

a(0) =3a(1) =16a(2) =67a(3) =251a(4) =888a(5) =3023a(6) =10038a(7) =32722a(8) =105228a(9) =334836a(10) =1056611a(11) =3311784a(12) =10322791a(13) =32026810a(14) =98974177a(15) =304835956a(16) =936147219a(17) =2867586542a(18) =8764280567a(19) =26733395986a(20) =81399821915a(21) =247459136331a(22) =751211286356