Place where n-th 1 occurs in A007336.

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =17a(5) =25a(6) =34a(7) =44a(8) =56a(9) =69a(10) =84a(11) =100a(12) =117a(13) =136a(14) =156a(15) =178a(16) =201a(17) =226a(18) =252a(19) =279a(20) =308a(21) =338a(22) =370a(23) =403a(24) =437a(25) =473a(26) =510a(27) =549a(28) =589a(29) =631