Cluster series for cubic lattice.

Terms

a(0) =1a(1) =6a(2) =30a(3) =114a(4) =438a(5) =1542a(6) =5754a(7) =19574a(8) =71958a(9) =233574a(10) =870666a(11) =2696274a(12) =10375770a(13) =30198116a(14) =122634404a(15) =327024444a(16) =1460721616a(17) =3347244554a(18) =17795165832