a(n) is the number of column convex polyiamonds with n cells.

Terms

a(0) =2a(1) =3a(2) =6a(3) =14a(4) =36a(5) =94a(6) =246a(7) =645a(8) =1682a(9) =4367a(10) =11312a(11) =29261a(12) =75654a(13) =195607a(14) =505794a(15) =1307977a(16) =3382628a(17) =8748288a(18) =22625594a(19) =58516858a(20) =151343298a(21) =391422104a(22) =1012341602