Number of spanning trees on the bipartite graph K_{3,n}.

Terms

a(0) =0a(1) =1a(2) =12a(3) =81a(4) =432a(5) =2025a(6) =8748a(7) =35721a(8) =139968a(9) =531441a(10) =1968300a(11) =7144929a(12) =25509168a(13) =89813529a(14) =312487308a(15) =1076168025a(16) =3673320192a(17) =12440502369a(18) =41841412812a(19) =139858796529a(20) =464904586800