Interactive practice questions
Write down the next $3$3 triangular numbers.
$1$1, $3$3, $6$6, $10$10, $15$15, $\editable{}$, $\editable{}$, $\editable{}$
Easy
< 1min
Beginning with the eighth triangular number, write down the next $3$3 triangular numbers is this series.
Easy
< 1min
Find the $6$6th triangular number.
Medium
1min
Find the $9$9th triangular number.
Medium
< 1min
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