Number of 2Xn 0..1 arrays with row sums nondecreasing and column sums unimodal.

Terms

a(0) =3a(1) =11a(2) =35a(3) =98a(4) =260a(5) =643a(6) =1563a(7) =3631a(8) =8407a(9) =18833a(10) =42313a(11) =92621a(12) =203973a(13) =439525a(14) =954373a(15) =2033480a(16) =4369630a(17) =9232317a(18) =19680561a(19) =41311764a(20) =87507822a(21) =182738699a(22) =385095795a(23) =800788788a(24) =1680371358a(25) =3482028637a(26) =7280492521a(27) =15041978366