<strike><h1> [Clojure], 58 bytes </h1>

<!-- language-all: lang-clj -->

    (fn[s](-(Math/pow(reduce + s)2)(reduce +(map #(* % %)s))))

[Try it online!][TIO-jo3kj47c]

[Clojure]: https://clojure.org/
[TIO-jo3kj47c]: https://tio.run/##S87JzyotSv3/XyMtL7o4VkNXwzexJEO/IL9coyg1pTQ5VUFboVjTSBPO08hNLFBQ1tBSUFVQ1SzWBIL//wE "Clojure – Try It Online"
</strike>


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## Edit: I misunderstood the question

# [Clojure], 55 bytes

<!-- language-all: lang-clj -->

    #(-(Math/pow(* %(+ % 1)1/2)2)(*(+ % 1)%(+(* 2 %)1)1/6))

[Try it online!][TIO-jo50cevr]

[Clojure]: https://clojure.org/
[TIO-jo50cevr]: https://tio.run/##S87JzyotSv3/X1lDV8M3sSRDvyC/XENLQVVDW0FVwVDTUN9I00hTQwvKBQoDJY0UVDVBUmaamv//AwA "Clojure – Try It Online"