Sum of digits of n-th triangular number.

Terms

a(0) =0a(1) =1a(2) =3a(3) =6a(4) =1a(5) =6a(6) =3a(7) =10a(8) =9a(9) =9a(10) =10a(11) =12a(12) =15a(13) =10a(14) =6a(15) =3a(16) =10a(17) =9a(18) =9a(19) =10a(20) =3a(21) =6a(22) =10a(23) =15a(24) =3a(25) =10a(26) =9a(27) =18a(28) =10a(29) =12