Squares of numbers of rooted trees.

Terms

a(0) =1a(1) =1a(2) =4a(3) =16a(4) =81a(5) =400a(6) =2304a(7) =13225a(8) =81796a(9) =516961a(10) =3392964a(11) =22714756a(12) =155900196a(13) =1087218729a(14) =7710771721a(15) =55404215161a(16) =403030713409