Number of 2Xn arrays containing n copies of 0..2-1 with row sums and column sums nondecreasing.

Terms

a(0) =1a(1) =4a(2) =5a(3) =15a(4) =21a(5) =57a(6) =85a(7) =220a(8) =341a(9) =858a(10) =1365a(11) =3368a(12) =5461a(13) =13276a(14) =21845a(15) =52479a(16) =87381a(17) =207861a(18) =349525a(19) =824527a(20) =1398101a(21) =3274395a(22) =5592405a(23) =13015081a(24) =22369621a(25) =51769813a(26) =89478485a(27) =206045841a(28) =357913941a(29) =820475513