a(n) = Sum_{k=0..2n} (k+1)*T(n,k), where T is given by A026536.

Terms

a(0) =1a(1) =4a(2) =18a(3) =48a(4) =180a(5) =432a(6) =1512a(7) =3456a(8) =11664a(9) =25920a(10) =85536a(11) =186624a(12) =606528a(13) =1306368a(14) =4199040a(15) =8957952a(16) =28553472a(17) =60466176a(18) =191476224a(19) =403107840a(20) =1269789696a(21) =2660511744a(22) =8344332288a(23) =17414258688a(24) =54419558400a(25) =113192681472a(26) =352638738432a(27) =731398864896