Science quiz
Triangular numbers: the first 20
Add 1, then 2, then 3, and keep going. Type the first 20 triangular numbers in order; each fills as soon as it is right.
- Format
- Type them all
- Items
- 20 answers
- Limit
- 2:30
- Level
- Medium
- Checked
- 2026.10.03
- Answers
- 20
- Time limit
- 2:30
- Order
- One at a time, no skipping
- Matching
- Case and accents ignored
- Answer each item in turn; the next appears when you get it right.
- Press Enter to check a guess.
- Pause whenever you like (Esc). The board hides while the clock is stopped.
Type the triangular numbers in order.
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
- Not reached yet
About this quiz
The nth triangular number is the sum of the whole numbers from 1 to n: the number of dots in a triangle with n dots along each side.
- The 20th triangular number is 210.
- Two neighbouring triangular numbers always add up to a square number.
- The formula is n times n plus 1, divided by 2.
More quizzes like this
| No. | Quiz | Section | Format | Items | Added |
|---|---|---|---|---|---|
| 01 | The Fibonacci sequence: first 20 numbers Type the first 20 numbers of the Fibonacci sequence in order, starting 1, 1, 2, 3, 5. Each one is the sum of the two before it. Science / Type them all / 20 answers | Science | Type them all | 20 | 2026.10.03 |
| 02 | What comes next? 20 number sequences 2, 4, 8, 16, 32 and then? Twenty number sequences, five terms each. Spot the rule and type the sixth term. Science / Type them all / 20 answers | Science | Type them all | 20 | 2026.10.03 |
| 03 | Click only the triangular numbers Click every one of the triangular numbers from 1 to 100, and nothing else. There are 13 in the grid, and one wrong click ends the game. Science / Click the grid / 13 to click | Science | Click the grid | 13 | 2026.10.03 |