Number of (n+1) X 3 binary arrays with every 2 X 2 subblock nonsingular.

Terms

a(0) =12a(1) =32a(2) =80a(3) =208a(4) =528a(5) =1360a(6) =3472a(7) =8912a(8) =22800a(9) =58448a(10) =149648a(11) =383440a(12) =982032a(13) =2515792a(14) =6443920a(15) =16507088a(16) =42282768a(17) =108311120a(18) =277442192a(19) =710686672a(20) =1820455440a(21) =4663202128a(22) =11945023888a(23) =30597832400a(24) =78377927952a(25) =200769257552