Number of order-5 ribbon tilings for a 5 X n strip.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =360a(6) =1140a(7) =3810a(8) =13434a(9) =49946a(10) =169024a(11) =574844a(12) =1970274a(13) =6826161a(14) =23977111a(15) =82657670a(16) =284973586a(17) =983395989a(18) =3400594524a(19) =11800532430a(20) =40796408747a(21) =141019980545a(22) =487480906364