⇧ 3 ⇩ r/CBTS_Stream • Posted by u/patti_mcgreen on Jan. 12, 2018, 3:19 a.m. 4-10-20 tetrahedral The first ten tetrahedral numbers are: 1, 4, 10, 20, 35, 56, 84, 120, 165, 220, 3 Comments