So in another sense we need numbers that add to 6:-
15,24,33,42,51,114,123,132,141,213,222,231,321,312,411,
1113,1122,1131,1212,1311,2112,2121,3111,11112,11121,11211,12111,21111,111111,

In another sense we can say that all those numbers have a Digital Root of 6.
IF you want to find out more about these digital roots see this article.