X1Xn

x1xn is not a standardized mathematical object with a single fixed definition. In practice, the string commonly appears as a schematic way to refer to a collection of variables indexed from 1 to n, or to a vector whose components are x1, x2, ..., xn. The exact interpretation depends on the surrounding context.

As a vector or sequence: In linear algebra and statistics, a data point or variable vector is often written as x = (x1, x2, ..., xn). Here x1, x2, ..., xn denote the coordinates or components of the vector. The shorthand x1..xn or x_{1..n} is sometimes used informally to indicate the entire sequence of components or the subvector consisting of the first n entries.

As a subscript range: In formulas, the notation x_{1..n} can denote the subsequence or subvector containing components with indices from 1 to n. This is common in discussions of sequences, arrays, or indexed families of variables.

Other uses: In programming or algorithmic contexts, x1xn may appear as a naming pattern for variables that vary over a range, though formal mathematical writing typically prefers explicit indices or structured data types to avoid ambiguity.

See also: index notation, index set, vector, sequence, product notation (∏). When encountering x1xn, it is best to interpret it from the surrounding material, as the exact meaning can vary between disciplines and authors.