# Python Math: Print the first n Lucky Numbers

## Python Math: Exercise-17 with Solution

Write a Python program to print the first n Lucky Numbers.

Lucky numbers are defined via a sieve as follows.

Begin with a list of integers starting with 1 :

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, . . . .

Now eliminate every second number :

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, ...

The second remaining number is 3, so remove every 3rd number:

1, 3, 7, 9, 13, 15, 19, 21, 25, ...

The next remaining number is 7, so remove every 7th number:

1, 3, 7, 9, 13, 15, 21, 25, ...

Next, remove every 9th number and so on.

Finally, the resulting sequence is the lucky numbers.

Following animation demonstrating the lucky number sieve. The numbers in red are lucky numbers.

Animation Credits: Celtic Minstrel

**Sample Solution**:-

**Python Code:**

```
n=int(input("Input a Number: "))
List=range(-1,n*n+9,2)
i=2
while List[i:]:List=sorted(set(List)-set(List[List[i]::List[i]]));i+=1
print(List[1:n+1])
```

Sample Output:

Input a Number: 10 [1, 3, 7, 9, 13, 15, 21, 25, 31, 33]

**Flowchart:**

## Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

**Python Code Editor:**

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**Previous:** Write a Python program to print all permutations of a given string (including duplicates).

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## Python: Tips of the Day

**Getting rid of unwanted characters:**

You can get rid of whitespaces or any specific character using strip methods in Python. You can use either plain strip for both sides, lstrip for the left side and rstrip for the right side only.

str="+++Welcome python+++" str.strip() print(str)

Output:

+++Welcome python+++

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