a(n) = Sum_{k=0..2n} (k+1) * A026584(n, k).

Terms

a(0) =1a(1) =4a(2) =18a(3) =56a(4) =190a(5) =564a(6) =1722a(7) =4976a(8) =14454a(9) =40940a(10) =115698a(11) =322728a(12) =896558a(13) =2471588a(14) =6786090a(15) =18537184a(16) =50459366a(17) =136844892a(18) =370030434a(19) =997705240a(20) =2683514526a(21) =7201203988a(22) =19284880794a(23) =51546789456a(24) =137541880150a(25) =366412976332