Number
31
- Positive
- Odd
- Prime
- 2 digits
31 is an odd 2-digit integer and a prime number. It has 2 divisors and a digital root of 4.
Number properties
ParityOddnot divisible by 2
SignPositive
PrimalityPrime
Absolute value31
Digit count2
Digit sum4
Digital root4repeated digit sum
PalindromicNoreads differently backwards
Happy numberYessquared-digit sums reach 1
Harshad numberNodivisible by its own digit sum
Factors & divisors
Prime factorisation31
Distinct prime factors131
Number of divisors2
Sum of divisors σ(n)32
Aliquot sum1sum of the proper divisors
ClassificationDeficientthe aliquot sum is less than the number
Euler's totient φ(n)30integers below n that share no factor with it
SquarefreeYesno repeated prime factor
All divisors1, 312 in total
Arithmetic
Representations
Decimal31
Binary111115 bits
Octal37
Hexadecimal1F
Base 36V
Roman numeralXXXI
In wordsthirty-one
Ordinalthirty-first
Scientific notation3.1 × 10^1
Engineering notation31
Nearest landmarks
Powers & multiples
31 to the power 2961
31 to the power 329,791
31 to the power 4923,521
31 to the power 528,629,151
First ten multiples31, 62, 93, 124, 155, 186, 217, 248, 279, 310
Powers of twoBetween 2^4 (16) and 2^5 (32)
Divisibility tests
Divisible by 2No, remainder 1
Divisible by 3No, remainder 1
Divisible by 4No, remainder 3
Divisible by 5No, remainder 1
Divisible by 6No, remainder 1
Divisible by 7No, remainder 3
Divisible by 8No, remainder 7
Divisible by 9No, remainder 4
Divisible by 10No, remainder 1
Divisible by 11No, remainder 9
Divisible by 12No, remainder 7
Divisible by 100No, remainder 31
Collatz (3n + 1) trajectory
Steps to reach 1106the total stopping time
Reaches 1Yesthe Collatz conjecture says every positive integer does, but it is unproven
First steps31 → 94 → 47 → 142 → 71 → 214 → 107 → 322 → 161 → 484 → …
Last steps… → 5 → 16 → 8 → 4 → 2 → 1
As a percentage & fraction
As a percentage3,100%
31% as a decimal0.31
31% of 10031
31% of 1,000310
As a fraction of 10031/100
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