Number of diamond polyominoes with n cells.

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =20a(5) =62a(6) =204a(7) =709a(8) =2526a(9) =9212a(10) =33989a(11) =126838a(12) =476597a(13) =1802618a(14) =6850969a(15) =26153537a(16) =100207548a(17) =385225375a(18) =1485216987a(19) =5741272625a(20) =22246000726a(21) =86383442996a(22) =336093551268