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1. Print Primes 1 to N2. Sum of Primes in Range3. Count Composite Numbers4. Twin Primes5. Goldbach Conjecture (Even as Sum of Two Primes)6. Prime Factors of Number7. Sum of Prime Factors8. Numbers with Prime Number of Factors9. Semi-Prime Numbers10. Prime Triplets

Count Composite Numbers

Count composite numbers in range.

IntermediatePhase 6 - Category 3: Loop & Conditional MixExample 3 of 10
count-composite-numbers.py
1# Helper function
2def is_prime(n):
3    if n < 2:
4        return False
5    for i in range(2, int(n ** 0.5) + 1):
6        if n % i == 0:
7            return False
8    return True
9

10# Take range
11a = int(input("Enter start: "))
12b = int(input("Enter end: "))
13

14# Count composites
15count = 0
16for num in range(a, b + 1):
17    if num > 1 and not is_prime(num):
18        count += 1
19

20print(f"Composite numbers: {count}")

Output

Enter start: 1
Enter end: 20
Composite numbers: 11

What's going on

Count numbers that are not prime.

Key Concepts:

Composite = not prime and > 1
Check each number
Count composites

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