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Question: Again, please figure out the answer
1=5
2=15
3=215
4=3215
5=?
Answer: 43215
Analysis: This level is purely about finding the rules between them. The mathematical formula between them is:
an=(n-1)*10^(n-1)+(n-2)*10^(n-2)+(n-3)*10^(n-3)+...+1* 10^1+5
a5=43215;
It can also be seen as each number has a units digit of 5, and the number on the largest digit (the digit of the Nth number) is N-1, followed by N-2, N-3, N-4.. ....all the way to 3,2,1, and then the ones digit is 5