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.
The canonical address for this page is /31.
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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Derived from 31
Other readings
Also reads as
#000031 (colour)
- #000031
- Blue
- Dark
- Nearest: Midnight blue
#000031 is a blue with RGB values 0, 0, 49 and HSL 240°, 100%, 10%. It is a dark colour, so white text on it reaches 20.1:1 contrast (AAA for normal text). The nearest named colour is Midnight blue.
Colour values
#000031#000031
HEX#000031
RGBrgb(0, 0, 49)
RGB (0–1)0, 0, 0.1922
RGB percentages0%, 0%, 19.2%
HSLhsl(240, 100%, 9.6%)
HSV / HSBhsv(240, 100%, 19.2%)
CMYK100%, 100%, 0%, 80.8%≈naive device-independent conversion; real print needs an ICC profile
24-bit integer49
CSS custom property--colour: #000031;
Brightness & contrast
Relative luminance0.00222WCAG 2.x, 0 is black and 1 is white
Perceived brightness16.5 of 255ITU-R BT.601 weighting
Light or darkDark
Best text colour on this backgroundWhitecontrast 20.11:1
Contrast with white20.11:1WCAG normal text: AAA
Contrast with black1.04:1WCAG normal text: Fail
Greyscale equivalent#040404
Inverted#FFFFCE
Colour vision & accessibility
Distinguishable without hueYesnever rely on hue alone to carry meaning
Contrast with white, large text20.11:1WCAG large text: AAA
Contrast with black, large text1.04:1WCAG large text: Fail
Named colours
Hue familyblue
CSS keyword usableNo exact keyword
Colour harmonies
Complementary#313100
Analogous#001931, #190031
Triadic#310000, #003100
Split complementary#311900, #193100
Tetradic#310019, #313100, #003119
Tints, shades & saturation
Channel breakdown
R0
G0
B49
Red0 (0%)
Green0 (0%)
Blue49 (19.2%)
Hue240°
Saturation (HSL)100%
Lightness9.61%
Dominant channelBlue
Hex per channelR 00 · G 00 · B 31
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Harmonies
Similar named colours
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