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factorial2
Double factorial function.
The double factorial of a number n
, denoted n!!
, is defined as the product of all the positive integers up to n
that have the same parity (odd or even) as n
.
Thus, for example, 5!!
is 5 * 3 * 1 = 15
and 8!!
is 8 * 6 * 4 * 2 = 384
.
Installation
npm install @stdlib/math-base-special-factorial2
Usage
var factorial2 = require( '@stdlib/math-base-special-factorial2' );
factorial2( n )
Evaluates the double factorial of n
.
var v = factorial2( 2 );
// returns 2
v = factorial2( 3 );
// returns 3
v = factorial2( 0 );
// returns 1
v = factorial2( 4 );
// returns 8
v = factorial2( 5 );
// returns 15
v = factorial2( NaN );
// returns NaN
v = factorial2( 301 );
// returns Infinity
Examples
var oneTo = require( '@stdlib/array-base-one-to' );
var factorial2 = require( '@stdlib/math-base-special-factorial2' );
var values = oneTo( 300 );
var i;
for ( i = 0; i < values.length; i++ ) {
console.log( 'f(%d): %d', values[ i ], factorial2( values[ i ] ) );
}
See Also
-
@stdlib/math-base/special/factorial
: evaluate a factorial.
Notice
This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
Community
License
See LICENSE.
Copyright
Copyright © 2016-2024. The Stdlib Authors.