What are the triangular numbers between 50 and 100?

Answer 1

Triangular numbers are generated by the formula ( T_n = \frac{n(n + 1)}{2} ). The triangular numbers between 50 and 100 are 55, 66, 78, and 91. These correspond to ( T_{10} ) (55), ( T_{11} ) (66), ( T_{12} ) (78), and ( T_{13} ) (91).