Unbalanced strings of length n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =6a(5) =18a(6) =42a(7) =98a(8) =210a(9) =450a(10) =930a(11) =1922a(12) =3906a(13) =7938a(14) =16002a(15) =32258a(16) =64770a(17) =130050a(18) =260610a(19) =522242a(20) =1045506a(21) =2093058a(22) =4188162a(23) =8380418a(24) =16764930a(25) =33538050a(26) =67084290a(27) =134184962a(28) =268386306a(29) =536805378