Exponential self-convolution of numbers of trees on n nodes.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =18a(5) =46a(6) =128a(7) =372a(8) =1174a(9) =3820a(10) =13170a(11) =46714a(12) =172490a(13) =652758a(14) =2547196a(15) =10156810a(16) =41495158a(17) =172810254a(18) =734132414a(19) =3171713642a(20) =13933910250a(21) =62121022408a(22) =280907384318