Number
18
- Positive
- Even
- Composite
- 2 digits
18 is an even 2-digit integer and a composite number. It has 6 divisors and a digital root of 9.
Number properties
ParityEvendivisible by 2
SignPositive
PrimalityComposite
Absolute value18
Digit count2
Digit sum9
Digital root9repeated digit sum
PalindromicNoreads differently backwards
Happy numberNosquared-digit sums reach 1
Harshad numberYesdivisible by its own digit sum
Factors & divisors
Prime factorisation2 × 3^2
Distinct prime factors22, 3
Number of divisors6
Sum of divisors σ(n)39
Aliquot sum21sum of the proper divisors
ClassificationAbundantthe aliquot sum exceeds the number
Euler's totient φ(n)6integers below n that share no factor with it
SquarefreeNohas a repeated prime factor
All divisors1, 2, 3, 6, 9, 186 in total
Arithmetic
Representations
Decimal18
Binary100105 bits
Octal22
Hexadecimal12
Base 36I
Roman numeralXVIII
In wordseighteen
Ordinaleighteenth
Scientific notation1.8 × 10^1
Engineering notation18
Nearest landmarks
Powers & multiples
18 to the power 2324
18 to the power 35,832
18 to the power 4104,976
18 to the power 51,889,568
First ten multiples18, 36, 54, 72, 90, 108, 126, 144, 162, 180
Powers of twoBetween 2^4 (16) and 2^5 (32)
Divisibility tests
Divisible by 2Yes
Divisible by 3Yes
Divisible by 4No, remainder 2
Divisible by 5No, remainder 3
Divisible by 6Yes
Divisible by 7No, remainder 4
Divisible by 8No, remainder 2
Divisible by 9Yes
Divisible by 10No, remainder 8
Divisible by 11No, remainder 7
Divisible by 12No, remainder 6
Divisible by 100No, remainder 18
Collatz (3n + 1) trajectory
Steps to reach 120the total stopping time
Reaches 1Yesthe Collatz conjecture says every positive integer does, but it is unproven
First steps18 → 9 → 28 → 14 → 7 → 22 → 11 → 34 → 17 → 52 → …
Last steps… → 5 → 16 → 8 → 4 → 2 → 1
As a percentage & fraction
As a percentage1,800%
18% as a decimal0.18
18% of 10018
18% of 1,000180
As a fraction of 10018/100
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