Bisection of A007059.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =43a(5) =140a(6) =472a(7) =1628a(8) =5719a(9) =20388a(10) =73562a(11) =268066a(12) =984911a(13) =3643570a(14) =13557020a(15) =50691978a(16) =190353370a(17) =717457656a(18) =2713061899a(19) =10289600164a(20) =39127877886a(21) =149147692734a(22) =569767908076