Number of 3D walks of type aad.

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =23a(5) =71a(6) =251a(7) =883a(8) =3305a(9) =12505a(10) =48895a(11) =193755a(12) =783355a(13) =3205931a(14) =13302329a(15) =55764413a(16) =236174933a(17) =1008773269a(18) =4343533967a(19) =18834033443a(20) =82201462251a(21) =360883031291