Number of 1-sided polytans (polyaboloes) with n cells.

Terms

a(0) =1a(1) =4a(2) =6a(3) =22a(4) =56a(5) =198a(6) =624a(7) =2182a(8) =7448a(9) =26319a(10) =92826a(11) =332181a(12) =1192845a(13) =4315845a(14) =15678200a(15) =57227380a(16) =209623109a(17) =770516966a(18) =2840466846a(19) =10499678185a(20) =38905008340a(21) =144475534207