The generalized Conway-Guy sequence d_2(n).

Terms

a(0) =1a(1) =2a(2) =6a(3) =16a(4) =48a(5) =140a(6) =408a(7) =1224a(8) =3640a(9) =10824a(10) =32192a(11) =96576a(12) =288912a(13) =864288a(14) =2585584a(15) =7735104a(16) =23205312a(17) =69551552a(18) =208461504a(19) =624806688a(20) =1872691488a(21) =5612903296a(22) =16838709888a(23) =50500659456a(24) =151455567744a(25) =454227600128