a(n) = position of the n-th n in A026409.

Terms

a(0) =1a(1) =4a(2) =9a(3) =18a(4) =27a(5) =40a(6) =55a(7) =72a(8) =89a(9) =113a(10) =140a(11) =167a(12) =194a(13) =221a(14) =253a(15) =294a(16) =329a(17) =369a(18) =419a(19) =452a(20) =502a(21) =552a(22) =618a(23) =677a(24) =721a(25) =776a(26) =836a(27) =894a(28) =976a(29) =1049