Witt vector *2!.

Terms

a(0) =2a(1) =1a(2) =4a(3) =13a(4) =44a(5) =135a(6) =472a(7) =1492a(8) =5324a(9) =17405a(10) =63944a(11) =215096a(12) =799416a(13) =2752909a(14) =10310384a(15) =36443256a(16) =137263244a(17) =489166324a(18) =1860249448a(19) =6739795717a(20) =25596173800a(21) =93596253769a(22) =357974884304