Exponentiation of e.g.f. for trees A000055(n-1).

Terms

a(0) =1a(1) =2a(2) =5a(3) =15a(4) =53a(5) =211a(6) =938a(7) =4582a(8) =24349a(9) =139671a(10) =858745a(11) =5628789a(12) =39145021a(13) =287667582a(14) =2226033629a(15) =18082308403a(16) =153770703339