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A base with a bracketed or underlined superscript, a product of descending terms.
Also known as: Falling factorial, Descending factorial, Pochhammer symbol, Factorial power
The falling factorial multiplies n by n−1 by n−2 and so on for a fixed number of terms, which is exactly the count of ordered selections without replacement. Its notation is a genuine mess: at least four incompatible spellings are in current use.
Denotes the product of a descending run of consecutive integers of specified length.
Contexts: Mathematics
Counts ordered selections without replacement, which is what makes it the permutation count in disguise.
Contexts: Mathematics
Has no settled notation: (x)_n, x^(n) with an underline, x_n with a bar and the Pochhammer bracket are all used, and two of them mean the rising factorial in other texts.
Contexts: Mathematics
A letter carrying a small parenthesised or underlined numeral raised to its upper right.