Boustrophedon transform of even numbers.

Terms

a(0) =0a(1) =2a(2) =8a(3) =24a(4) =72a(5) =240a(6) =924a(7) =4116a(8) =20944a(9) =119952a(10) =763540a(11) =5346748a(12) =40845816a(13) =338041704a(14) =3012855356a(15) =28770647220a(16) =293055401888