Number of symmetrical n-celled polyominoes.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =7a(5) =15a(6) =24a(7) =53a(8) =89a(9) =194a(10) =323a(11) =722a(12) =1197a(13) =2706a(14) =4465a(15) =10229a(16) =16814a(17) =38900a(18) =63721a(19) =148808a(20) =243006a(21) =571937a(22) =931305a(23) =2207561a(24) =3584959a(25) =8551309a(26) =13851410a(27) =33229843a(28) =53694326a(29) =129485500