Number
51
- Positive
- Odd
- Composite
- 2 digits
51 is an odd 2-digit integer and a composite number. It has 4 divisors and a digital root of 6.
Number properties
ParityOddnot divisible by 2
SignPositive
PrimalityComposite
Absolute value51
Digit count2
Digit sum6
Digital root6repeated digit sum
PalindromicNoreads differently backwards
Happy numberNosquared-digit sums reach 1
Harshad numberNodivisible by its own digit sum
Factors & divisors
Prime factorisation3 × 17
Distinct prime factors23, 17
Number of divisors4
Sum of divisors σ(n)72
Aliquot sum21sum of the proper divisors
ClassificationDeficientthe aliquot sum is less than the number
Euler's totient φ(n)32integers below n that share no factor with it
SquarefreeYesno repeated prime factor
All divisors1, 3, 17, 514 in total
Arithmetic
Representations
Decimal51
Binary1100116 bits
Octal63
Hexadecimal33
Base 361F
Roman numeralLI
In wordsfifty-one
Ordinalfifty-first
Scientific notation5.1 × 10^1
Engineering notation51
Nearest landmarks
Powers & multiples
51 to the power 22,601
51 to the power 3132,651
51 to the power 46,765,201
51 to the power 5345,025,251
First ten multiples51, 102, 153, 204, 255, 306, 357, 408, 459, 510
Powers of twoBetween 2^5 (32) and 2^6 (64)
Divisibility tests
Divisible by 2No, remainder 1
Divisible by 3Yes
Divisible by 4No, remainder 3
Divisible by 5No, remainder 1
Divisible by 6No, remainder 3
Divisible by 7No, remainder 2
Divisible by 8No, remainder 3
Divisible by 9No, remainder 6
Divisible by 10No, remainder 1
Divisible by 11No, remainder 7
Divisible by 12No, remainder 3
Divisible by 100No, remainder 51
Collatz (3n + 1) trajectory
Steps to reach 124the total stopping time
Reaches 1Yesthe Collatz conjecture says every positive integer does, but it is unproven
First steps51 → 154 → 77 → 232 → 116 → 58 → 29 → 88 → 44 → 22 → …
Last steps… → 5 → 16 → 8 → 4 → 2 → 1
As a percentage & fraction
As a percentage5,100%
51% as a decimal0.51
51% of 10051
51% of 1,000510
As a fraction of 10051/100
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