T(n,n-3), array T as in A047120.

Terms

a(0) =1a(1) =2a(2) =6a(3) =28a(4) =120a(5) =501a(6) =2020a(7) =8062a(8) =31992a(9) =126556a(10) =499478a(11) =1968504a(12) =7751812a(13) =30513489a(14) =120090702a(15) =472636988a(16) =1860354732a(17) =7323975621a(18) =28840527086a(19) =113600162826a(20) =447592682400