Number of paraffins C_n H_{2n-1} X_3 with n carbon atoms.

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =14a(5) =39a(6) =109a(7) =312a(8) =890a(9) =2552a(10) =7325a(11) =21047a(12) =60465a(13) =173750a(14) =499068a(15) =1433071a(16) =4113105a(17) =11799780a(18) =33834367a(19) =96968462a(20) =277771344a(21) =795310628a(22) =2276055442a(23) =6510786627a(24) =18616389094a(25) =53207964655a(26) =152014267327a(27) =434136228215