Number of 1-sided strip polytans with n cells.

Terms

a(0) =1a(1) =4a(2) =6a(3) =21a(4) =47a(5) =134a(6) =323a(7) =876a(8) =2224a(9) =5885a(10) =15146a(11) =39574a(12) =102250a(13) =265574a(14) =686208a(15) =1775646a(16) =4583718a(17) =11835037a(18) =30515520a(19) =78652647