a(n) = C(n)-1+0^n where C(n) = A000108(n).

Terms

a(0) =1a(1) =0a(2) =1a(3) =4a(4) =13a(5) =41a(6) =131a(7) =428a(8) =1429a(9) =4861a(10) =16795a(11) =58785a(12) =208011a(13) =742899a(14) =2674439a(15) =9694844a(16) =35357669a(17) =129644789a(18) =477638699a(19) =1767263189a(20) =6564120419a(21) =24466267019a(22) =91482563639a(23) =343059613649