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The symbol looks like a mirrored capitalized E.
Because I don't know its name, I cannot Google for it.

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    It's a fair question since you would have to know Greek or math notation. Can be found here here, and here.
    – Peter
    Feb 16, 2016 at 13:46
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    Note that almost all math symbols are Greek letters, so if you find another one you want to know the name of, just check the Greek alphabet: en.wikipedia.org/wiki/Greek_alphabet#Letters Feb 16, 2016 at 17:17
  • Lists of mathematical symbols also help. E.g., the capital sigma for summation that you're looking for is available in this list. Something like Detexify may help, too, although it won't necessarily tell you the name of the symbol, it may well help. Feb 16, 2016 at 18:59
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    Your description "mirrored capitalized E" would more accurately describe the existential quantification operator than the summation operator IMHO Feb 16, 2016 at 19:10
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    Not relevant to the question, which is about the English language, but the equation in the question is incorrect (unless N=0). For example, taking k=2 makes the claim "N/2+N/4 = 2N", which is clearly false. Feb 17, 2016 at 0:03

1 Answer 1

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It is an upper case Sigma, from the Greek alphabet.

It is almost always used to denote a summation:

and is therefore (technically) called a summation symbol, as others pointed out in the comments.

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    Yes! Therefore the usual English name of this mathematical symbol (in this context) is summation symbol, summation sign, or summation operator. The related Unicode character for this use is ∑ (U+2211) and called n-ary summation (where "n-ary" is a generic term generalizing "unary", "binary", "ternary" etc.). In contrast the usual Greek letter has another character Σ (U+03A3) which is called Greek captal letter sigma. Feb 16, 2016 at 15:57
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    And read out loud (as part of a complete phrase, not pointing out the symbol itself) it's simply "sum". As in "The sum from k equals 0 to 5 of k"
    – hobbs
    Feb 16, 2016 at 23:40
  • While it's true that the symbol is a Greek capital sigma, it is much more appropriate to describe it as a summation sign. Feb 16, 2016 at 23:59
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    @hobbs I thought it was "the sum of k from k equals 0 to 5"?
    – tox123
    Feb 17, 2016 at 3:07
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    @lovespring yes, it should be either this, or "I don't know it's name, so I cannot Google for it". The words "because" and "so" have the same function in this context.
    – Glorfindel
    Feb 17, 2016 at 7:43

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