The revolver sequence.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =3a(6) =4a(7) =5a(8) =18a(9) =43a(10) =60a(11) =84a(12) =294a(13) =472a(14) =724a(15) =1077a(16) =3504a(17) =5807a(18) =10396a(19) =15944a(20) =43664a(21) =84308a(22) =137004a(23) =217728a(24) =582966a(25) =1134304a(26) =1883360a(27) =3225812a(28) =8964134a(29) =15461472