(* Triangular numbers *)

M=5;
Column[Table[o,{m,1,M},{n,1,m}],Center]

M=5;
Column[Table[o,{m,1,M},{n,1,m}]]

Table[Column[Table[o,{m,1,M},{n,1,m}]],{M,1,5}]

Table[Column[Table[o,{m,1,M},{n,1,m}],Center],{M,1,5}]

Manipulate[Column[Table[o,{m,1,M},{n,1,m}]],{M,1,10}]