Positive integer solutions of $(591-b-c-d)^2+(591-b-c-d)+41 = bcd$

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Is there a non-numerical way to find the positive integer solutions of this equation: $(591-b-c-d)^2+(591-b-c-d)+41 = bcd$ ?

Numerically I know the answer is $b=47,c=53,d=71$ or a permutation of these values.

Any help would be appreciated.

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The hint.

Show that $a^2+a+41$ is a prime number for all $2\leq a\leq39.$

Also, $a=40$ and $a=41$ they are not valid and for some numbers $a>41$ we get that $a^2+a+41$ is also prime.

Also, by AM-GM $$a^2+a+41\leq\left(\frac{591-a}{3}\right)^3,$$ which gives $a\leq422.$