Series Completion: 13, 35, 57, 79, 911, ?

Concept: In a concatenation-type number series, a term is not obtained by an arithmetic operation (addition, multiplication) on the previous term. Instead, each term is formed by writing two consecutive odd numbers side by side, and the pair of odd numbers used advances by one step for every new term.

1. The base sequence of odd numbers is 1, 3, 5, 7, 9, 11, 13, ...

2. Joining 1 and 3 side by side gives the first term: 13.

3. Joining 3 and 5 gives the second term: 35.

4. Joining 5 and 7 gives the third term: 57.

5. Joining 7 and 9 gives the fourth term: 79.

6. Joining 9 and 11 gives the fifth term: 911.

7. Continuing the same rule, the next pair after (9, 11) is (11, 13); joining them gives 1113.

Cross-check: each pair's first number matches the previous pair's second number (3→3, 5→5, 7→7, 9→9, 11→11), confirming the odd-number sequence advances one term at a time without skipping or repeating any number; only 1113 is consistent with this rule.