Number of nX2 0..2 arrays with the row and column sums nondecreasing.

Terms

a(0) =6a(1) =32a(2) =133a(3) =510a(4) =1792a(5) =6050a(6) =19641a(7) =62471a(8) =194925a(9) =601743a(10) =1839745a(11) =5593544a(12) =16923954a(13) =51060524a(14) =153682210a(15) =461909664a(16) =1386731666a(17) =4160516211a(18) =12476101149a(19) =37401839918a(20) =112103310741a(21) =335973601041