2, 5, 10, 17, __?

Step-by-step solution

1. Notice the differences between consecutive terms: $5-2=3$, $10-5=5$, $17-10=7$.
2. The differences increase by $2$ each time: $3,5,7,dots$
3. The next difference is $7+2=9$.
4. Add this to the last term: $17+9=26$.
5. So the missing number is $26$.

Concept tested: Identify increasing difference pattern

Published 1 October 2026 · How this solution was prepared and checked