Self-convolution of numbers of trees on n nodes.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =7a(5) =12a(6) =23a(7) =44a(8) =90a(9) =186a(10) =407a(11) =902a(12) =2072a(13) =4844a(14) =11595a(15) =28150a(16) =69491a(17) =173522a(18) =438423a(19) =1117968a(20) =2875960a(21) =7453070a(22) =19447591a(23) =51050224a(24) =134749849a(25) =357446716a(26) =952527403a(27) =2548897192a(28) =6846986075a(29) =18458150242