Number of 3-bead necklaces where each bead is an unlabeled rooted tree, by total number of nodes.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =18a(6) =43a(7) =103a(8) =255a(9) =642a(10) =1640a(11) =4242a(12) =11096a(13) =29278a(14) =77882a(15) =208589a(16) =562056a(17) =1522606a(18) =4144521a(19) =11329608a(20) =31090910a(21) =85618848a(22) =236530942a(23) =655344579a(24) =1820585313a(25) =5070138554a(26) =14151907583a(27) =39584395796a(28) =110938500821a(29) =311481097178