Duplicate of A009490.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =6a(6) =9a(7) =11a(8) =14a(9) =16a(10) =20a(11) =23a(12) =27a(13) =31a(14) =35a(15) =43a(16) =47a(17) =55a(18) =61a(19) =70a(20) =78a(21) =88a(22) =98a(23) =111a(24) =123