Given positive integers $a \le b \le c \le d$, it may be possible to form quadrilaterals with edge lengths $a,b,c,d$ (in any order). When this is the case, let $M(a,b,c,d)$ denote the maximal area of such a quadrilateral.
For example, $M(2,2,3,3)=6$, attained e.g. by a $2\times 3$ rectangle.
Let $SP(n)$ be the sum of $a+b+c+d$ over all choices $a \le b \le c \le d$ for which $M(a,b,c,d)$ is a positive integer not exceeding $n$.
$SP(10)=186$ and $SP(100)=23238$.
Find $SP(1\,000\,000)$.
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