Jac(n)(2Jac(n)-1).

Terms

a(0) =0a(1) =1a(2) =1a(3) =15a(4) =45a(5) =231a(6) =861a(7) =3655a(8) =14365a(9) =58311a(10) =232221a(11) =932295a(12) =3725085a(13) =14913991a(14) =59639581a(15) =238612935a(16) =954386205a(17) =3817763271a(18) =15270790941a(19) =61084037575a(20) =244335101725a(21) =977343902151