Number of fixed snake polyominoes with n cells.

Terms

a(0) =1a(1) =2a(2) =6a(3) =14a(4) =34a(5) =82a(6) =198a(7) =470a(8) =1122a(9) =2662a(10) =6334a(11) =14970a(12) =35506a(13) =83734a(14) =198086a(15) =466314a(16) =1100818a(17) =2587634a(18) =6097830a(19) =14316402a(20) =33687146a(21) =79008870a(22) =185677006a(23) =435098774a(24) =1021404998a(25) =2391646494a(26) =5609151738a(27) =13125214770a(28) =30757286802a(29) =71928506630