I want to share a series of questions that are created by myself.
I will give a hint in 24 hours and my answer in 3 days given that nobody could answer my question.
Here is my number sequence:
2020,1436,7575,?,23111311
If you guys want some extremely challenging questions. Please check these two questions posted by me.
Number sequences: 000, X00... and 6X000X9, 700XX08
What are the alphabets in the question mark?
Update
Hint1:
The logic is related to 1234
Hint2:
Separate the digits
The missing number is
$69811$
Procedure for getting from one step to the next
1. Separate out the digits (e.g, $2020 \rightarrow 2,0,2,0$).
2. Reverse the sequence (e.g, $2,0,2,0 \rightarrow 0,2,0,2$).
3. Add $1$ to the first digit, $2$ to the second, $\ldots n$ to the $n$th (e.g, $0,2,0,2 \rightarrow 1,4,3,6$).
4. Recombine the digits (e.g, $1,4,3,6 \rightarrow 1436$).
Other cases, step-by-step
$1436 \rightarrow 7575$
1. $1436 \rightarrow 1,4,3,6$
2. $1,4,3,6 \rightarrow 6,3,4,1$
3. $6,3,4,1 \rightarrow 7,5,7,5$
4. $7,5,7,5 \rightarrow 7575$
$7575 \rightarrow 69811$
1. $7575 \rightarrow 7,5,7,5$
2. $7,5,7,5 \rightarrow 5,7,5,7$
3. $5,7,5,7 \rightarrow 6,9,8,11$
4. $6,9,8,11 \rightarrow 69811$
$69811 \rightarrow 23111311$
1. $69811 \rightarrow 6,9,8,1,1$
2. $6,9,8,1,1 \rightarrow 1,1,8,9,6$
3. $1,1,8,9,6 \rightarrow 2,3,11,13,11$
4. $2,3,11,13,11 \rightarrow 23111311$
