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Question

# A number n is said to be 'perfect' if the sum of all its divisors (excluding n itself) is equal to n. An example of a perfect number is915216

A
6
B
9
C
15
D
21
Solution
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#### Lets check each option one by one A. 9 divisor are 1 and 3. 1+3=4≠9 so not a perfect number.B. 15 divisors are 1,3, and 5. 1+3+5=9≠15 so not a perfect numberC. 21 divisors are 1, 3 and 7. 1+3+7=11≠21, so not a perfect number.D. 6 divisors are 1,2 and 3. 1+2+3=6 It is a perfect number So correct answer is option D

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