Multifactorial Calculator
Compute the factorial n!, double factorial n!!, triple factorial n!!!, and the general multifactorial n!k — with every multiplication step shown and exact results for large n.
Worked examples
Frequently asked questions
What is a multifactorial?
A multifactorial generalizes the ordinary factorial. The multifactorial n!_k of order k multiplies n by every k-th smaller positive integer: n × (n−k) × (n−2k) × … down to the last term above zero. The ordinary factorial n! is the special case k = 1.
What is 7!! (7 double factorial)?
7!! = 7 × 5 × 3 × 1 = 105. A double factorial uses order k = 2, so it multiplies every second integer counting down from n.
What is 8!! (8 double factorial)?
8!! = 8 × 6 × 4 × 2 = 384. Even double factorials end at 2, while odd ones end at 1.
What is 9!!! (9 triple factorial)?
9!!! = 9 × 6 × 3 = 162. A triple factorial uses order k = 3, stepping down by 3 each time.
How is 5! calculated step by step?
5! = 5 × 4 × 3 × 2 × 1 = 120. The factorial multiplies every whole number from n down to 1.
What is 0! (zero factorial)?
0! = 1. By convention the empty product equals 1, which keeps formulas such as combinations consistent when n = 0.
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