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I've been looking in vain (most books I came across give identities involving sums or recurrence relations, but do not give much attention to fixed values) for a reference to the following identity: $S(n,n-3)={n \choose 2}{n \choose 4},$ where $S(n,k)$ is the unsigned Stirling number of the first kind. Is this well-known, or too trivial to be mentioned anywhere?

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    It's not trivial, but the constant, 3, is just big enough not to be important enough to be even an exercise in a text. But it's perfect for OEIS as noted below.2011-03-02

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The identity and the proof for the identity are there in the wiki link you have sent.

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    Also noted at [OEIS A001303](http://oeis.org/A001303) which has other formulae and several references to the sequence2011-03-02