Number of free polyominoes of width 3 and height n.

Terms

a(0) =1a(1) =6a(2) =24a(3) =181a(4) =941a(5) =4662a(6) =23691a(7) =119271a(8) =603760a(9) =3050402a(10) =15428576a(11) =78004550a(12) =394462578a(13) =1994595585a(14) =10086050889a(15) =51001111356a(16) =257894037378