Number of tilings of a 4 X n rectangle using integer-sided rectangular tiles of equal area.

Terms

a(0) =1a(1) =3a(2) =9a(3) =20a(4) =49a(5) =115a(6) =343a(7) =850a(8) =2401a(9) =6698a(10) =18677a(11) =52383a(12) =148417a(13) =418280a(14) =1184717a(15) =3357537a(16) =9518235a(17) =27001128a(18) =76637532a(19) =217530615a(20) =617624137a(21) =1753811531a(22) =4980521844a(23) =14144892243a(24) =40174244540a(25) =114105904403a(26) =324101321331a(27) =920579535645