a(n) = 10 + floor( (1 + Sum_{j=1..n-1} a(j) )/3 ).

Terms

a(0) =10a(1) =13a(2) =18a(3) =24a(4) =32a(5) =42a(6) =56a(7) =75a(8) =100a(9) =133a(10) =178a(11) =237a(12) =316a(13) =421a(14) =562a(15) =749a(16) =999a(17) =1332a(18) =1776a(19) =2368a(20) =3157a(21) =4209a(22) =5612a(23) =7483a(24) =9977a(25) =13303a(26) =17737a(27) =23650a(28) =31533a(29) =42044