Number of 1-sided polyrhombs with n cells.

Terms

a(0) =1a(1) =2a(2) =4a(3) =13a(4) =35a(5) =120a(6) =392a(7) =1405a(8) =4998a(9) =18378a(10) =67792a(11) =253509a(12) =952534a(13) =3604624a(14) =13699554a(15) =52304807a(16) =200406370a(17) =770442286a(18) =2970401696a(19) =11482513428a(20) =44491881033a(21) =172766765654a(22) =672186650116