Analog of A095236 when the phones are arranged in a circle.

Terms

a(0) =1a(1) =2a(2) =6a(3) =8a(4) =40a(5) =96a(6) =168a(7) =384a(8) =1728a(9) =15360a(10) =50688a(11) =221184a(12) =299520a(13) =1290240a(14) =3628800a(15) =30965760a(16) =65802240a(17) =743178240a(18) =7060193280a(19) =237817036800a(20) =624269721600