Number of isomers C_n H_{2n} without double bonds.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =5a(5) =12a(6) =29a(7) =73a(8) =185a(9) =475a(10) =1231a(11) =3232a(12) =8506a(13) =22565a(14) =60077a(15) =160629a(16) =430724a(17) =1158502a(18) =3122949a(19) =8437289a(20) =22836877a(21) =61918923a(22) =168139339a(23) =457225555a(24) =1244935251a(25) =3393754661a(26) =9261681937a(27) =25301337669a(28) =69184724389a(29) =189349490641