This sequence appears to be a set of numbers that could follow a mathematical pattern. Let's analyze the numbers:

$5, 12, 13, 10, ?, 26$

1. Check for differences or ratios:

   • From 5 to 12: $12 - 5 = 7$
   • From 12 to 13: $13 - 12 = 1$
   • From 13 to 10: $13 - 10 = 3$
   • From 10 to the missing value (?): let's denote the difference as $x$.
   • From the missing value (?) to 26: let's denote the difference as $y$.

2. Check for patterns: The differences are alternating in size, which suggests it may not be purely an arithmetic progression, but rather a shifting or alternating pattern.

We could investigate further, but based on these clues and patterns in common mathematical sequences, the missing number could be $17$, assuming an alternating addition and subtraction pattern.

Thus, the complete sequence would be: $5, 12, 13, 10, 17, 26$

Let me know if you'd like further details or have any questions!

Here are 5 related questions to explore this topic further:

1. What is the difference between arithmetic and geometric sequences?
2. How can you determine if a sequence is quadratic?
3. What are Fibonacci numbers, and could they fit this pattern?
4. What is the general form of a recursive sequence?
5. How do we find the formula for a sequence when given a few terms?

Tip: When analyzing number patterns, always check for common sequences (arithmetic, geometric, Fibonacci) and then look for any alternating or recursive patterns.