Function
src/index.ts:791nerdamer.dfactorial
nerdamer.dfactorial(x: Expression): ExpressionComputes the double factorial of an expression. For a non-negative integer n, the double factorial is the product of all positive integers up to n that share its parity: - Even:
`n!! = 2 · 4 · 6 · … · n`- Odd:
`n!! = 1 · 3 · 5 · … · n`For non-integer arguments when
`Settings.EVALUATE`is
`true`, a generalised formula using the gamma function is applied.
throws
UndefinedError If
`x`is
`-∞`.
Parameters
| Name | Type | Description |
|---|---|---|
x | Expression | The expression to compute the double factorial of. |
Returns
Expression — The double factorial of `x`.
Examples
doubleFactorial(Expression.create(6)).text() // "48"
doubleFactorial(Expression.create(7)).text() // "105"