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 Unitary perfect numbers (Posted on 2013-12-16)
A unitary divisor of a number n is a number d such that d|n and gcd(d, n/d)=1. For example, 3 is a unitary divisor of 12 because gcd(3, 12/3)=gcd(3, 4)=1.

A unitary perfect number is a number that is the sum of its unitary divisors less than itself. For example, 60 is a unitary perfect number because its unitary divisors less than itself are 1, 3, 4, 5, 12, 15, and 20, and 1+3+4+5+12+15+20=60. Find all unitary perfect numbers less than 1000000.

 See The Solution Submitted by Math Man Rating: 5.0000 (1 votes)

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 re: just look up - spoiler | Comment 5 of 10 |

I respectfully disagree with my co-solver Ady.  Just because a puzzle can be looked up in OEIS, that doesn't mean that the problem is trivial.  I would rate this somewhere between D3 and D4, which is the same rating I would have given before OEIS or the internet existed.

Thanks, Math Man!

 Posted by Steve Herman on 2013-12-16 19:37:23

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