Number of unlabeled alternating octopuses with n black nodes.

Terms

a(0) =2a(1) =9a(2) =26a(3) =85a(4) =274a(5) =981a(6) =3498a(7) =13005a(8) =48818a(9) =186193a(10) =716474a(11) =2782657a(12) =10878642a(13) =42792797a(14) =169181578a(15) =671878845a(16) =2678679362a(17) =10716700257a(18) =43007271770a(19) =173072733629a(20) =698235687858