# Again Pythagoras

Consider the triplets of positive integers $$(a,b,c)$$ with $$a$$ is odd, $$\gcd(a,b,c)=1$$ and $$a^2+b^2=c^2$$.

Which one can't be a value of $$b$$?

 Notation: $$\gcd(\cdot)$$ denotes the greatest common divisor function.

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