Triangular Numbers Calculator
What happens when geometry and abstract math meet? Discover it with the triangular number calculator!
T1055the sum 1 + 2 + … + 10
Formula10 × 11 ÷ 2 = 55
Next triangular number66
Also a square number?No
Sum of two consecutive triangulars121always a perfect square
Nearby triangular numbers
| T5 | 15 |
| T6 | 21 |
| T7 | 28 |
| T8 | 36 |
| T9 | 45 |
| T10 | 55 |
| T11 | 66 |
| T12 | 78 |
| T13 | 91 |
The method
Tₙ = n(n + 1) ÷ 2