Number of signed trees with n nodes.

Terms

a(0) =1a(1) =2a(2) =3a(3) =10a(4) =27a(5) =98a(6) =350a(7) =1402a(8) =5743a(9) =24742a(10) =108968a(11) =492638a(12) =2266502a(13) =10600510a(14) =50235931a(15) =240882152a(16) =1166732814a(17) =5702046382a(18) =28088787314a(19) =139355139206a(20) =695808554300