Summation Symbol (∑)

Summation Symbol uses ∑, U+2211 N-ARY SUMMATION, as a large mathematical operator for adding an indexed family of terms. In a formula such as ∑ᵢ₌₁ⁿ i, the lower expression identifies the starting index, the upper expression gives the final value, and the term to the right is the summand. The operator therefore needs its bounds and summand to be read as one complete construction. Typical uses include finite sums, infinite series, statistical totals, and compact derivations. Examples such as ∑ᵢ xᵢ, Mean = (1/n)∑xᵢ, and Total = ∑ category values show why the surrounding equation matters. A bare ∑ does not tell the reader what is being added or over which range. In inline prose, short limits may remain readable, but complex limits are better handled with equation markup so that the index and bounds stay attached to the operator. The most common substitution error is typing Greek capital sigma Σ instead of ∑. Although the shapes are related, Σ is a letter and ∑ is the n-ary summation operator. The neighboring operators ∏ and ∐ also have different functions: ∏ denotes repeated multiplication, while ∐ is used for a coproduct. A font may make these forms look similar, so checking U+2211 is more reliable than judging appearance alone. Formatting should state the index variable and its range, define the summand, and preserve grouping around the expression. Use selectable text or mathematical markup rather than a screenshot when the formula itself is the content. For HTML, ∑ may be entered literally, as ∑, or as ∑. After export to PDF, slides, or a content-management system, verify that the operator and its limits have not been separated. They do not make ∑ interchangeable with Σ or with every large symbol used in a mathematical display.