The number of Hamiltonian cycles in the concentric ring graph of order n.

Terms

a(0) =6a(1) =12a(2) =30a(3) =34a(4) =56a(5) =108a(6) =150a(7) =244a(8) =418a(9) =642a(10) =1040a(11) =1712a(12) =2726a(13) =4412a(14) =7174a(15) =11554a(16) =18696a(17) =30292a(18) =48950a(19) =79204a(20) =128202a(21) =207362a(22) =335520a(23) =542936a(24) =878406a(25) =1421292a(26) =2299758a(27) =3720994a(28) =6020696a(29) =9741756