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Omni-MATH / Call a sequence of positive integers {a_(n)} good if for any distinct positive integers m,n, one has gcd(m,n)∣a_(m)²+a_(n)² and gcd(a_(m),a_(n))∣m²+n². Call a positive integer a to…

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Call a sequence of positive integers {an}\{a_n\} good if for any distinct positive integers m,nm,n, one has gcd(m,n)am2+an2 and gcd(am,an)m2+n2.\gcd(m,n) \mid a_m^2 + a_n^2 \text{ and } \gcd(a_m,a_n) \mid m^2 + n^2. Call a positive integer aa to be kk-good if there exists a good sequence such that ak=aa_k = a. Does there exists a kk such that there are exactly 20192019 kk-good positive integers?
Plain-text mathematical notation (without MathML)
Call a sequence of positive integers {a_(n)} good if for any distinct positive integers m,n, one has 
gcd(m,n)∣a_(m)²+a_(n)² and gcd(a_(m),a_(n))∣m²+n².
Call a positive integer a to be k-good if there exists a good sequence such that a_(k)=a. Does there exists a k such that there are exactly 2019 k-good positive integers?
Original LaTeX notation
Call a sequence of positive integers $\{a_n\}$ good if for any distinct positive integers $m,n$, one has 
$$\gcd(m,n) \mid a_m^2 + a_n^2 \text{ and } \gcd(a_m,a_n) \mid m^2 + n^2.$$
Call a positive integer $a$ to be $k$-good if there exists a good sequence such that $a_k = a$. Does there exists a $k$ such that there are exactly $2019$ $k$-good positive integers?

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