Tuesday, 22 April 2014

Finding three numbers that are pairwise not relatively prime, but with gcd(a,b,c)=1



Find integers a,b, and c where gcd(a,b,c)=1, but gcd(a,b)1, gcd(a,c)1, and gcd(b,c)1.



I tried so many combinations but I can't find 3 integers that meet these requirements.




I even though (0,0,0) works, because I tried to convince myself 1 is the first positive integer where 0 has a divisor, because you can't divide by 0. I am not sure if there is a more systematic approach to this.


Answer



Consider a=6,b=10,c=15



An easy way to construct these is by considering three prime 2,3,5, then pairwise multiply them.


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