a(n) = Phi(Bell(n)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =8a(5) =24a(6) =168a(7) =876a(8) =1056a(9) =11232a(10) =92760a(11) =180944a(12) =4010832a(13) =27644436a(14) =93648672a(15) =1101958000a(16) =10436655840a(17) =27621623160a(18) =584607107256