Exercise · ZW-PERFECT-NUMBER-001 · ★☆☆ Basic

Which of these numbers is perfect?

Choose one option.

Show answer
  • D. 6

Explanation

The proper divisors of 6 sum to \(1+2+3=6\). The number 4 gives 3, 9 gives 4, and 10 gives 8, none equal to the number itself.

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Review the concept: Perfect number

A perfect number is a positive integer \(n\) equal to the sum of its proper divisors, those smaller than \(n\); with the divisor-sum function \(\sigma\), the sum of all its divisors is twice \(n\).

\[\sigma(n)=2n\]

More practice problems: perfect number

ZW-PERFECT-NUMBER-002 →