Partial sums of A028356.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =13a(5) =15a(6) =16a(7) =18a(8) =21a(9) =25a(10) =28a(11) =30a(12) =31a(13) =33a(14) =36a(15) =40a(16) =43a(17) =45a(18) =46a(19) =48a(20) =51a(21) =55a(22) =58a(23) =60a(24) =61a(25) =63a(26) =66a(27) =70a(28) =73a(29) =75