Number of nX3 0,1 arrays with the row and column sums nondecreasing.

Terms

a(0) =4a(1) =17a(2) =66a(3) =235a(4) =824a(5) =2848a(6) =9520a(7) =31648a(8) =104536a(9) =339553a(10) =1099666a(11) =3549038a(12) =11338836a(13) =36160324a(14) =115069316a(15) =363700188a(16) =1148126044a(17) =3619072821a(18) =11352513438a(19) =35579368776a(20) =111388887136a(21) =347450537496