Sequence with a (4,-8) Somos-4 Hankel transform.

Terms

a(0) =1a(1) =0a(2) =2a(3) =-2a(4) =8a(5) =-20a(6) =64a(7) =-200a(8) =656a(9) =-2184a(10) =7408a(11) =-25456a(12) =88480a(13) =-310464a(14) =1098304a(15) =-3912896a(16) =14026752a(17) =-50557184a(18) =183110400a(19) =-666079872a(20) =2432399104a(21) =-8914099840a(22) =32772922112a(23) =-120844493056a(24) =446793362944