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

Terms

a(0) =3a(1) =9a(2) =9a(3) =33a(4) =53a(5) =183a(6) =395a(7) =1249a(8) =3141a(9) =9459a(10) =25655a(11) =75639a(12) =212943a(13) =623093a(14) =1787609a(15) =5222369a(16) =15134933a(17) =44250051a(18) =128996855a(19) =377748883a(20) =1105350731a(21) =3242546393a(22) =9513228125a(23) =27953744695a(24) =82176836303a(25) =241834027353a(26) =712070156205