a(n) = floor(n^((n-1)/2)).

Terms

a(0) =1a(1) =1a(2) =3a(3) =8a(4) =25a(5) =88a(6) =343a(7) =1448a(8) =6561a(9) =31622a(10) =161051a(11) =861979a(12) =4826809a(13) =28172943a(14) =170859375a(15) =1073741824a(16) =6975757441a(17) =46753733110a(18) =322687697779