The SET® card game is played with a pack of $81$ distinct cards. Each card has four features (Shape, Color, Number, Shading). Each feature has three different variants (e.g. Color can be red, purple, green).

A SET consists of three different cards such that each feature is either the same on each card or different on each card.

For a collection $C_n$ of $n$ cards, let $S(C_n)$ denote the number of SETs in $C_n$. Then define $F(n)=\sum _{C_n}S(C_n{)}^4$ where $C_n$ ranges through all collections of $n$ cards (among the $81$ cards). You are given $F(3)=1080$ and $F(6)=159690960$.

Find $F(12)$.

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