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.

, 6,60, 90, 87360,
146361946186458562560000 (sequence A002827 in OEIS)<o:p></o:p>

Apparently, none others are known

Rem:  does not qualify as a D3 puzzle

Posted by Ady TZIDON on 2013-12-16 14:52:26