Factorial Calculator

Calculate n factorial, double factorial, subfactorial, trailing zeros, and digit count with large number support.

Non-negative integer (n)

Enter a non-negative integer (0 to 10,000).

Enter a number to calculate.

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Double Factorial (0!!)

Subfactorial (!0)

Trailing Zeros

Digit Count

Max n:

n	n!	Digits

Formulae

n! = 1 × 2 × 3 × ... × n (0! = 1)

n!! = product of every second integer down from n

!n = (n−1)(·!(n−1) + !(n−2)), !0 = 1, !1 = 0

Trailing zeros = Σ floor(n / 5^k) for k = 1, 2, 3, ...

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Enter a number

Type a non-negative integer.
2

View the results

See n!, double factorial, subfactorial, trailing zeros, and digit count instantly.
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Explore the table

Toggle table mode to see factorials for a range of values.

What is the largest factorial I can compute?

The tool uses BigInt for exact results, so it handles very large values. Display may truncate extremely long numbers.

What is a subfactorial?

The subfactorial !n counts derangements — permutations where no element appears in its original position.

How are trailing zeros counted?

Count how many times 10 divides n!, which equals the sum of floor(n/5^k) for k=1,2,3...

Is my data sent anywhere?

No. All calculations run in your browser.

Compute factorials and related functions. Enter a non-negative integer

to calculate n!, double factorial (n!!), subfactorial (!n, derangements),

trailing zero count, and digit count. Supports large values using BigInt.

Table mode shows n! for a range of values. All processing runs in your

browser.

Find the greatest common divisor and least common multiple of two or more numbers with step-by-step prime factorization.

Check if a number is prime, find its prime factorization, list primes in a range, or find the Nth prime number.