Number of skew shapes in a 3 X n rectangle with no empty rows or columns.

Terms

a(0) =1a(1) =8a(2) =29a(3) =73a(4) =151a(5) =276a(6) =463a(7) =729a(8) =1093a(9) =1576a(10) =2201a(11) =2993a(12) =3979a(13) =5188a(14) =6651a(15) =8401a(16) =10473a(17) =12904a(18) =15733a(19) =19001a(20) =22751a(21) =27028a(22) =31879a(23) =37353a(24) =43501a(25) =50376a(26) =58033a(27) =66529a(28) =75923a(29) =86276