Number of 3 X 3 0..n arrays with row and column sums one greater than the previous row and column.

Terms

a(0) =2a(1) =42a(2) =228a(3) =776a(4) =2046a(5) =4578a(6) =9128a(7) =16704a(8) =28602a(9) =46442a(10) =72204a(11) =108264a(12) =157430a(13) =222978a(14) =308688a(15) =418880a(16) =558450a(17) =732906a(18) =948404a(19) =1211784a(20) =1530606a(21) =1913186a(22) =2368632a(23) =2906880a(24) =3538730a(25) =4275882a(26) =5130972a(27) =6117608a(28) =7250406a(29) =8545026