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| | Harmonic divisor number - Open Encyclopedia (Site not responding. Last check: 2007-10-08) |
 | | 1, 6, 28, 140, 270, 496, 672, 1638, 2970, 6200, 8128, 8190 |
 | | Three of these listed are also perfect numbers, and like perfect numbers, harmonic divisor numbers tend to even numbers, at least in the range observed. |
 | | For example, 496 is a harmonic divisor number because 496 divided by the sum of the reciprocals of its divisors, 1, 2, 4, 8, 16, 31, 62, 124, 248 and 496, (the harmonic mean), yields an integer, 5 in this case. |
| www.open-encyclopedia.com /Harmonic_divisor_number (130 words) |
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