Number of fixed polybends with n cells.

Terms

a(0) =4a(1) =8a(2) =16a(3) =29a(4) =52a(5) =96a(6) =176a(7) =310a(8) =556a(9) =1000a(10) =1800a(11) =3159a(12) =5612a(13) =9992a(14) =17788a(15) =31160a(16) =55076a(17) =97452a(18) =172424a(19) =301752a(20) =531460a(21) =936684a(22) =1650924a(23) =2886702a(24) =5071604a(25) =8914664a(26) =15670616a(27) =27380368a(28) =48016600a(29) =84237912