Number of Baxter matrices of size 3 X n that contain n+2 1's.

Terms

a(0) =1a(1) =8a(2) =26a(3) =55a(4) =96a(5) =149a(6) =214a(7) =291a(8) =380a(9) =481a(10) =594a(11) =719a(12) =856a(13) =1005a(14) =1166a(15) =1339a(16) =1524a(17) =1721a(18) =1930a(19) =2151a(20) =2384a(21) =2629a(22) =2886a(23) =3155a(24) =3436a(25) =3729a(26) =4034a(27) =4351a(28) =4680a(29) =5021