a(n) is equal to a(n-1) plus (a(n-1) written in base n but interpreted in base n+1), with a(1)=1.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =19a(5) =41a(6) =87a(7) =193a(8) =427a(9) =940a(10) =2049a(11) =4619a(12) =10363a(13) =22921a(14) =50522a(15) =111018a(16) =248438a(17) =554112a(18) =1232067a(19) =2723158a(20) =6003186a(21) =13446356a(22) =30050952a(23) =66594552a(24) =147234100a(25) =324832999a(26) =714046741a(27) =1585188074a(28) =3511557725a(29) =7762753394