Number of tatami tilings of a 4 X n grid (with monomers allowed).

Terms

a(0) =1a(1) =5a(2) =29a(3) =44a(4) =66a(5) =126a(6) =238a(7) =490a(8) =922a(9) =1714a(10) =3306a(11) =6246a(12) =12102a(13) =22994a(14) =43682a(15) =83810a(16) =159154a(17) =305062a(18) =581382a(19) =1108362a(20) =2119602a(21) =4037338a(22) =7716554a(23) =14720142a(24) =28084702a(25) =53639778a(26) =102298794a(27) =195341594a(28) =372753634a(29) =711338798