Number of ways to tile a 4 X n region with 1 X 1 and 2 X 2 tiles.

Terms

a(0) =1a(1) =1a(2) =5a(3) =11a(4) =35a(5) =93a(6) =269a(7) =747a(8) =2115a(9) =5933a(10) =16717a(11) =47003a(12) =132291a(13) =372157a(14) =1047181a(15) =2946251a(16) =8289731a(17) =23323853a(18) =65624397a(19) =184640891a(20) =519507267a(21) =1461688413a(22) =4112616845a(23) =11571284395a(24) =32557042499a(25) =91602704493a(26) =257733967693a(27) =725161963867