Number patterns

The question

5, 17, ?, 41, 53

517?4153

517294153

Find the rule first, from two numbers you can actually see — never from the gap.
5 to 17 is + 12. One pair is a guess, though — check it against another.
41 + 12 = 53, so the rule holds. Two pairs agreeing is what turns a guess into the rule.
Now apply it to the gap: 17 + 12 = 29.
Check it against the number already after the gap: 29 + 12 = 41, which is what is there. The missing number is 29.

How it works.

01
Find the rule first, from two numbers you can actually see — never from the gap.
02
5 to 17 is + 12. One pair is a guess, though — check it against another.
03
41 + 12 = 53, so the rule holds. Two pairs agreeing is what turns a guess into the rule.
04
Now apply it to the gap: 17 + 12 = 29.
05
Check it against the number already after the gap: 29 + 12 = 41, which is what is there. The missing number is 29.