The number of fixed n-ominoes with a convex hull of width 3.

Terms

a(0) =1a(1) =8a(2) =31a(3) =95a(4) =269a(5) =721a(6) =1866a(7) =4728a(8) =11804a(9) =29162a(10) =71502a(11) =174342a(12) =423341a(13) =1024786a(14) =2474934a(15) =5966625a(16) =14365256a(17) =34550674a(18) =83035396a(19) =199440433a(20) =478814076a(21) =1149133511a(22) =2757142136a(23) =6613933242a(24) =15863281135a(25) =38042981575a(26) =91225540813a(27) =218739876078a(28) =524464594304