Duplicate of A104779.

Terms

a(0) =1a(1) =3a(2) =7a(3) =21a(4) =57a(5) =182a(6) =565a(7) =1931a(8) =6670a(9) =24537a(10) =92337a(11) =364602a(12) =1477148a(13) =6219031a(14) =26875932a(15) =119930947a(16) =548688443a(17) =2580814003a(18) =12425175838a(19) =61302331782a(20) =309055818656