Two terms are missing from the series 5, ?, 17, 29, ?, 65. Which pair of numbers fills the gaps, in order?

Explanation

1. 01

   Only one difference can be read directly: $29 - 17 = 12$, a multiple of 4. Try differences that grow by 4.

2. 02

   Try differences 4, 8, 12, 16, 20: $5 + 4 = 9$, $9 + 8 = 17$, $17 + 12 = 29$, $29 + 16 = 45$, $45 + 20 = 65$.

3. 03

   Every known term fits, so the gaps are 9 and 45.