Problem 61014. Find nth number

Created by Le

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The numbers 2 and 7 are called lucky numbers, an integer containing only the digits 2 and 7 is also called lucky number. The problem is, given a sequence of lucky numbers arranged in the following order:
Lucky_num=[ 2, 7, 22, 27, 72, 77, 222, 227, 272, 277, 722, 727, 772, 777,.......]
Write a function that takes n as a parameter, we expect the output to be the nth lucky number
Eg: 
n=8
-> output: 227

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Last Solution submitted on Oct 23, 2025

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Christian Schröder on 19 Oct 2025 at 9:03

I think the test suite may be wrong: the 50th lucky number is 72277, the 110th is 727777, and the 500th is 77772727.

Le on 20 Oct 2025 at 5:11

thanks for pointing out the mistake, I forgot to round when creating the test case, the test case has been updated.

Ritik on 20 Oct 2025 at 10:38

It was intitially hard untill i saw the pattern.

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Problem 61014. Find nth number

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Problem 61014. Find nth number

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Last 200 Solutions

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