Number of ways to tile a 3 X n strip with squares and P-shaped heptominoes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =9a(4) =17a(5) =31a(6) =109a(7) =251a(8) =553a(9) =1527a(10) =3721a(11) =8799a(12) =22521a(13) =55607a(14) =135161a(15) =337655a(16) =835305a(17) =2051719a(18) =5086601a(19) =12580007a(20) =31019689a(21) =76724327a(22) =189674697a(23) =468351815a(24) =1157626473a(25) =2861142183a(26) =7068302665a(27) =17467362631a(28) =43166610985a(29) =106658791143