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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

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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. $2,3,11,13,11 \rightarrow 23111311$

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  • $\begingroup$ Yes, that is correct! I was about to post my own answer...I strongly recommend you to try the challenging ones! $\endgroup$ – LETTERKING May 20 at 16:02

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