Partial sums of repdigit numbers (A010785).

Terms

a(0) =0a(1) =1a(2) =3a(3) =6a(4) =10a(5) =15a(6) =21a(7) =28a(8) =36a(9) =45a(10) =56a(11) =78a(12) =111a(13) =155a(14) =210a(15) =276a(16) =353a(17) =441a(18) =540a(19) =651a(20) =873a(21) =1206a(22) =1650a(23) =2205a(24) =2871a(25) =3648a(26) =4536a(27) =5535a(28) =6646a(29) =8868