Extract using 7Zip, we see a flag.txt file protected by a password as well as another puzzle.png shown below:

There is a pattern to this puzzle, and it is nothing mathematical. From 12 to 11112, firstly, we put a 1, then we count how many of what numbers is in the previous line. In this case, there is one 1 and one 2. Thus, we append 11 and 12. We get: 11112

From 11112 to 24112, firstly, we put a 2, then we count how many of what numbers is in the previous line. In this case, there is four 1 and one 2. Thus, we append 41 and 12. We get: 24112

As we carry on, we get the ? to be 61542142311.

Extract flag.txt using the password above. We get:

R1pIUEdTe1EzeV9NM19RNDU3NHpfRTRzNzBfVzRhX1U0el9PMV9RM3kwX1c0YV9QdTAwYV9YMGE0en0=

Base 64 decoding gives us:

GZHPGS{Q3y_M3_Q4574z_E4s70_W4a_U4z_O1_Q3y0_W4a_Pu00a_X0a4z}

ROT13 to get the flag:

TMUCTF{D3l_Z3_D4574m_R4f70_J4n_H4m_B1_D3l0_J4n_Ch00n_K0n4m}

Original writeup (https://github.com/Rookie441/CTF/blob/main/Storage/Writeups/TMUCTF2021_Writeup.md#puzzle).