2*A000540.

Terms

a(0) =0a(1) =2a(2) =130a(3) =1588a(4) =9780a(5) =41030a(6) =134342a(7) =369640a(8) =893928a(9) =1956810a(10) =3956810a(11) =7499932a(12) =13471900a(13) =23125518a(14) =38184590a(15) =60965840a(16) =94520272a(17) =142795410a(18) =210819858a(19) =304911620a(20) =432911620a(21) =604443862a(22) =831203670a(23) =1127275448a(24) =1509481400a(25) =1997762650a(26) =2615594202a(27) =3390435180