a(n) = (1/2)*A290923(n).

Terms

a(0) =1a(1) =5a(2) =23a(3) =104a(4) =469a(5) =2115a(6) =9539a(7) =43024a(8) =194053a(9) =875245a(10) =3947651a(11) =17805240a(12) =80307649a(13) =362214635a(14) =1633710407a(15) =7368586016a(16) =33234813001a(17) =149900237685a(18) =676100727791