The fourth column of A038622, triangular array that counts rooted polyominoes.

Terms

a(0) =1a(1) =5a(2) =20a(3) =71a(4) =238a(5) =770a(6) =2436a(7) =7590a(8) =23397a(9) =71566a(10) =217646a(11) =659022a(12) =1988805a(13) =5986176a(14) =17980968a(15) =53922096a(16) =161492571a(17) =483149385a(18) =1444245936a(19) =4314214443a(20) =12880107548a(21) =38436170366a(22) =114657076900a(23) =341926185770