Place where n-th 1 occurs in A023122.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =15a(5) =22a(6) =30a(7) =39a(8) =49a(9) =61a(10) =74a(11) =88a(12) =103a(13) =119a(14) =137a(15) =156a(16) =176a(17) =197a(18) =220a(19) =244a(20) =269a(21) =295a(22) =322a(23) =351a(24) =381a(25) =412a(26) =444a(27) =478a(28) =513a(29) =549