Number of symmetric filaments (strip polyominoes) with n square cells.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =5a(6) =5a(7) =12a(8) =12a(9) =27a(10) =28a(11) =64a(12) =67a(13) =147a(14) =158a(15) =348a(16) =373a(17) =799a(18) =879a(19) =1886a(20) =2069a(21) =4335a(22) =4864a(23) =10204a(24) =11432a(25) =23488a(26) =26814a(27) =55179a(28) =62925a(29) =127133