product of all integers between 1 and the integral input of the function
FactorialReIm
In mathematics, the factorial of a non-negative integer ... {\displaystyle {\begin{aligned}n!&=n\times (n-1)\times (n-2)\times (n-3)\times \cdots \times 3\times 2\times 1\\&={\begin{cases}1,&{\text{if }}n=0\\n\times (n-1)!,&{\text{if }}n\geq 1.\end{cases}}\\\end{aligned}}} For example, ... ... … Wikipedia
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Wikipedia
en.wikipedia.org β€Ί wiki β€Ί Factorial
Factorial - Wikipedia
1 week ago - Factorials have been discovered in several ancient cultures, notably in Indian mathematics in the canonical works of Jain literature, and by Jewish mystics in the Talmudic book Sefer Yetzirah. The factorial operation is encountered in many areas of mathematics, notably in combinatorics, where its most basic use counts the possible distinct sequences – the permutations – of
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Reddit
reddit.com β€Ί r/explainlikeimfive β€Ί eli5: what is a factorial and how does it work
r/explainlikeimfive on Reddit: ELI5: What is a factorial and how does it work
December 31, 2024 - A way to understand what a factorial represents is that it's the number of ways you can arrange X items. for example if you had 6 teddy bears, and you lined them up, you'd have 6 choices for the first bear, 5 choices for the second bear, and so on.
People also ask

What is the meaning of 5 factorial?
The meaning of 5 factorial is that we need to multiply the numbers from 1 to 5. That means, 5! = 5 Γ— 4 Γ— 3 Γ— 2 Γ— 1 = 120.
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byjus.com
byjus.com β€Ί maths β€Ί factorial
Factorial
What is the symbol of factorial?
The factorial function is a mathematical formula represented by an exclamation mark β€œ!”. For example, the factorial of 8 can be represented as 8! and it is read as eight factorial.
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byjus.com
byjus.com β€Ί maths β€Ί factorial
Factorial
How do you calculate a factorial?
A factorial is calculated by starting with the number and multiplying it by each previous integer until reaching 1. The factorial is represented by an exclamation point. x! = x * (x-1) * (x-2) ...1. For example, 4! = 4 * 3 * 2 * 1 =24.
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study.com
study.com β€Ί courses β€Ί math courses β€Ί math 101: college algebra
Factorial | Definition, Examples & Operations - Lesson | Study.com
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BYJUS
byjus.com β€Ί maths β€Ί factorial
Factorial
In short, a factorial is a function that multiplies a number by every number below it till 1. For example, the factorial of 3 represents the multiplication of numbers 3, 2, 1, i.e. 3! = 3 Γ— 2 Γ— 1 and is equal to 6.
Published Β  October 6, 2021
Views Β  1K
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Purplemath
purplemath.com β€Ί modules β€Ί factorial.htm
What are factorials, and how do they work? | Purplemath
The factorial of a whole number n, denoted as n!, is the product of all the whole numbers between 1 and n: 1Γ—2Γ—3×…×(nβˆ’1)Γ—n. So 3! would be 1Γ—2Γ—3 = 6.
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Study.com
study.com β€Ί courses β€Ί math courses β€Ί math 101: college algebra
Factorial | Definition, Examples & Operations - Lesson | Study.com
July 9, 2012 - A factorial is a mathematical function represented by an exclamation mark, The symbol x! means to start with a positive integer, x, and multiply by each previous integer until reaching 1. The mathematical factorial definition is x!= x * (x-1) ...
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freeCodeCamp
freecodecamp.org β€Ί news β€Ί what-is-a-factorial
What is a Factorial? How to Calculate Factorials with Examples
August 3, 2022 - A factorial is a mathematical operation that you write like this: n!. It represents the multiplication of all numbers between 1 and n. So if you were to have 3!, for example, you'd compute 3 x 2 x 1 (which = 6). Let's see how it works with some more
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Cuemath
cuemath.com β€Ί numbers β€Ί factorial
Factorial - Meaning, Formula | Factorial of Hundred & 0
The first formula directly follows from factorial definition whereas the second formula means that the factorial of any number is, the given number, multiplied by the factorial of the previous number. So, 8! = 8 Γ— 7!...... And 9! = 9 Γ— 8!...... The factorial of 10 will be 10!
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Math is Fun
mathsisfun.com β€Ί numbers β€Ί factorial.html
Factorial Function !
The factorial function (symbol: !) says to multiply all whole numbers from our chosen number down to 1. Examples:
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CalculatorSoup
calculatorsoup.com β€Ί calculators β€Ί discretemathematics β€Ί factorials.php
Factorial Calculator n!
Factorial of 10 10! = 10 Γ— 9 Γ— 8 Γ— 7 Γ— 6 Γ— 5 Γ— 4 Γ— 3 Γ— 2 Γ— 1 = 3,628,800 ... A factorial is a function that multiplies a number by every number below it. For example 5!= 5*4*3*2*1=120.
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Encyclopedia Britannica
britannica.com β€Ί science β€Ί mathematics
Factorial | Definition, Symbol, & Facts | Britannica
July 20, 1998 - Factorial, in mathematics, the product of all positive integers less than or equal to a given positive integer and denoted by that integer and an exclamation point. Thus, factorial seven is written 7!, meaning 1 Γ— 2 Γ— 3 Γ— 4 Γ— 5 Γ— 6 Γ— 7. ...
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Indeed
indeed.com β€Ί career guide β€Ί career development β€Ί factorials: what are they, how to calculate them and examples
Factorials: What Are They, How To Calculate Them and Examples | Indeed.com
October 23, 2023 - A factorial is a function in mathematics with the symbol (!) that multiplies a number (n) by every number that precedes it. In simpler words, the factorial function says to multiply all the whole numbers from the chosen number down to one.
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Factorial US
factorialhr.com β€Ί number function factorial
The Factorial Function
If we have 4 colored pictures and want to hang them on the wall, one after another we can calculate the number of possible combinations: ... At this point, you may be wondering why Factorial chose that name for its human resources software. Well, Factorial represents growth to the last power, a ...
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GeeksforGeeks
geeksforgeeks.org β€Ί mathematics β€Ί factorial
Factorial in Maths: Definition, Formulas & Applications - GeeksforGeeks
The factorial of a number is the product of all positive integers from that number down to 1.
Published Β  December 29, 2025
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Corporate Finance Institute
corporatefinanceinstitute.com β€Ί home β€Ί resources β€Ί factorial
Factorial - Overview, Formula, Factors, Applications
November 14, 2024 - The factorial (denoted or represented as n!) for a positive number or integer (which is denoted by n) is the product of all the positive numbers
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Reddit
reddit.com β€Ί r/learnmath β€Ί what does factorial mean realistically ?
r/learnmath on Reddit: What does factorial mean realistically ?
June 12, 2020 -

Never bothered to understand maths ever, and am now reading cryptography as a hobby in spare time, so help me guys please.

I got that the factorial means just the product of numbers , eg : 4! = 4 Γ— 3 Γ— 2 Γ— 1

Lets say, take a letter for english alphabet and replace it with another random letter for eg :

A = I B = H

,then the books says the decryption keys will be equal to 26 factorial or 26! (since there are 26 letters in english alphabet)

This doesnt' make any sense whatsoever , if the question is too basic please point to another sub if possible. I googled the shit out of it and still don't get it.

Top answer
1 of 10
98
It is describing how many ways that a substitution key can be created. Walk through it this way. Assume that we start with A. What alphabet replaces 'A'. It could be anything from A to Z. So there are 26 choices of a substitute. OK. Let's for the purpose of this example say 'A's will be replaced by 'K'. Now go to B. What alphabet replaces B? Since we already assigned K to replace A, there are only 25 alphabets to choose from. By the time you get to Z, there will be only one unassigned substitute. So how many keys total? There are 26 choices from our starting point, then 25, then 24 all the way to 1. Therefore there are 26 * 25 * 24 *... * 1 ways of creating a unique key and this is called 26! from the definition of factorials.
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7
What the book is saying is that "there are 26 factorial possible keys for a simple substitution". To see why this is true let's go through part of the process: What will A be changed into? Well there are 26 possibilities. We could say that A doesn't change or we could say it changes into any other letter. Let's pick L and say A -> L is one of our rules. Now, what will B get changed into? There are only 25 possibilities left if we want the cipher to work. B can get changed to any letter except L because we've already decided that A turns into L. If B became L then when decoding there would be no way to know if L meant A or B. So let's make the rule B -> K. For C there are only 24 possibilities, following the same logic. And so on down to Z which will have only one option.
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Wolfram MathWorld
mathworld.wolfram.com β€Ί Factorial.html
Factorial -- from Wolfram MathWorld
September 13, 2025 - Another relationship between factorials and triangular numbers is given by the identity ... The factorial gives the number of ways in which objects can be permuted. For example, , since the six possible permutations of are , , , , , . The first few factorials for , 1, 2, ...
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Fonzi AI
fonzi.ai β€Ί blog β€Ί what-is-a-factorial
What Is a Factorial? Simple Definition + Examples - Fonzi AI Recruiter
August 14, 2025 - A factorial, represented by the exclamation mark (!), is the product of all positive integers from 1 up to a specific number. For instance, 5! equals 5 Γ— 4 Γ— 3 Γ— 2 Γ— 1, which results in 120.
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Statlect
statlect.com β€Ί glossary β€Ί factorial
Factorial | Use in probability and statistics
The expression is read " factorial". This definition is extended to the number 0 by using the convention: ... It is frequent to encounter ratios of factorials, which can be computed by simplifying the common terms.
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Cambridge Dictionary
dictionary.cambridge.org β€Ί dictionary β€Ί english β€Ί factorial
FACTORIAL | English meaning - Cambridge Dictionary
The 3 x 2 factorial study was designed to assess the efficacy and safety of 3 different dose levels of doxorubicin. ... The number is calculated as a multiplication 1 x 2 x 3 x 4 x 5 x 6=720, or expressed in factorial mathematics: 6!=720.
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Merriam-Webster
merriam-webster.com β€Ί dictionary β€Ί factorial
Definition of FACTORIAL
The meaning of FACTORIAL is of, relating to, or being a factor or a factorial.