a(n) = n + A000108(n-1) for n > 1; a(0)=0, a(1)=1.

Terms

a(0) =0a(1) =1a(2) =3a(3) =5a(4) =9a(5) =19a(6) =48a(7) =139a(8) =437a(9) =1439a(10) =4872a(11) =16807a(12) =58798a(13) =208025a(14) =742914a(15) =2674455a(16) =9694861a(17) =35357687a(18) =129644808a(19) =477638719a(20) =1767263210a(21) =6564120441a(22) =24466267042a(23) =91482563663a(24) =343059613674