Number of paraffins C_n H_{2n} X Y with n carbon atoms.

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =12a(5) =31a(6) =80a(7) =210a(8) =555a(9) =1479a(10) =3959a(11) =10652a(12) =28760a(13) =77910a(14) =211624a(15) =576221a(16) =1572210a(17) =4297733a(18) =11767328a(19) =32266801a(20) =88594626a(21) =243544919a(22) =670228623a(23) =1846283937a(24) =5090605118a(25) =14047668068a(26) =38794922293a(27) =107215238057a(28) =296501478704