Recognised as Number
666
- Positive
- Even
- Composite
- 3 digits
666 is an even 3-digit integer and a composite number. It has 12 divisors and a digital root of 9.
Number properties
ParityEvendivisible by 2
SignPositive
PrimalityComposite
Absolute value666
Digit count3
Digit sum18
Digit product216
Multiplicative persistence3times the digit product can be taken before one digit is left
Digital root9repeated digit sum
PalindromicYesreads the same backwards
Triangular numberYes, the 36th triangular number
Happy numberNosquared-digit sums reach 1
Harshad numberYesdivisible by its own digit sum
Factors & divisors
Prime factorisation2 × 3^2 × 37
Distinct prime factors32, 3, 37
Number of divisors12
Sum of divisors σ(n)1,482
Aliquot sum816sum of the proper divisors
ClassificationAbundantthe aliquot sum exceeds the number
Euler's totient φ(n)216integers below n that share no factor with it
Carmichael function λ(n)36the smallest exponent with aˣ ≡ 1 for every unit; smaller than φ(n) = 216
Möbius function μ(n)0zero, because a prime divides n twice
SquarefreeNohas a repeated prime factor
All divisors1, 2, 3, 6, 9, 18, 37, 74, 111, 222, 333, 66612 in total
Arithmetic
Representations
Decimal666
Binary101001101010 bits
Octal1232
Hexadecimal29A
Base 36II
Roman numeralDCLXVI
In wordssix hundred and sixty-six
Ordinalsix hundred and sixty-sixth
Scientific notation6.66 × 10^2
Engineering notation666
In other bases
Ternary220200base 3; the most digit-efficient integer base after e: 6 digits
Quinary10131base 5; one hand: 5 digits
Septenary1641base 7: 4 digits
Nonary820base 9; each digit is two ternary digits: 3 digits
Duodecimal476base 12; divides by 2, 3, 4 and 6, which is why eggs and inches come in twelves: 3 digits
Vigesimal1d6base 20; hands and feet, and the Mayan and Yoruba systems: 3 digits
Sexagesimal11:6base 60; Babylonian, and still how an hour and a circle are divided: 2 digits
Balanced ternary10T1T00digits −1, 0 and +1 written T, 0 and 1; negation is swapping T and 1, so no sign is needed
Negabinary11111101110base −2; place values alternate 1, −2, 4, −8, so every integer has exactly one form without a sign
Bit-level
0000001010011010
Bit length10 bitsto write the magnitude
Set bits5the population count, or Hamming weight
Zero bits5within that length
Bit parityodd5 set bits, so odd; not the same as the number itself being even
Highest set bitbit 9worth 512
Lowest set bitbit 11 trailing zero
Power of twoNo
Bytes202 9a
Gray code1111010111n XOR (n >> 1); successive values differ in exactly one bit
At each machine width
16-bit0000001010011010
32-bit00000000000000000000001010011010
64-bit0000000000000000000000000000000000000000000000000000001010011010
One's complement1111110101100101at 16 bits, every bit flipped
Bits reversed0101100101000000at 16 bits
Rotated left by 10000010100110100at 16 bits, wrapping
Shifted left by 110100110100= 1,332, no wrap
Shifted right by 1101001101= 333, discarding the low bit
These bits as a double3.2904772 × 10^-321≈IEEE-754 binary64 reinterpretation of the same 64 bits (subnormal)
Nearest landmarks
Powers & multiples
666 to the power 2443,556
666 to the power 3295,408,296
666 to the power 4196,741,925,136
666 to the power 5131,030,122,140,576
First ten multiples666, 1,332, 1,998, 2,664, 3,330, 3,996, 4,662, 5,328, 5,994, 6,660
Powers of twoBetween 2^9 (512) and 2^10 (1,024)
Divisibility tests
Divisible by 2Yes
Divisible by 3Yes
Divisible by 4No, remainder 2
Divisible by 5No, remainder 1
Divisible by 6Yes
Divisible by 7No, remainder 1
Divisible by 8No, remainder 2
Divisible by 9Yes
Divisible by 10No, remainder 6
Divisible by 11No, remainder 6
Divisible by 12No, remainder 6
Divisible by 100No, remainder 66
Collatz (3n + 1) trajectory
Steps to reach 1113the total stopping time
Reaches 1Yesthe Collatz conjecture says every positive integer does, but it is unproven
First steps666 → 333 → 1,000 → 500 → 250 → 125 → 376 → 188 → 94 → 47 → …
Last steps… → 5 → 16 → 8 → 4 → 2 → 1
As a percentage & fraction
As a percentage66,600%
666% as a decimal6.66
666% of 100666
666% of 1,0006,660
As a fraction of 100666/100
Read another way
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Derived from 666
Other readings
Also reads as
#666666 (colour)
- #666666
- Grey
- Dark
- Nearest: Dim grey
#666666 is a grey with RGB values 102, 102, 102 and HSL 0°, 0%, 40%. It is a dark colour, so white text on it reaches 5.7:1 contrast (AA for normal text). The nearest named colour is Dim grey.
Colour values
#666666#666666
HEX#666666
HEX (short)#666
RGBrgb(102, 102, 102)
RGB (0–1)0.4, 0.4, 0.4
RGB percentages40%, 40%, 40%
HSLhsl(0, 0%, 40%)
HSV / HSBhsv(0, 0%, 40%)
CMYK0%, 0%, 0%, 60%≈naive device-independent conversion; real print needs an ICC profile
24-bit integer6,710,886
CSS custom property--colour: #666666;
Brightness & contrast
Relative luminance0.13287WCAG 2.x, 0 is black and 1 is white
Perceived brightness102 of 255ITU-R BT.601 weighting
Light or darkDark
Best text colour on this backgroundWhitecontrast 5.74:1
Contrast with white5.74:1WCAG normal text: AA
Contrast with black3.66:1WCAG normal text: Fail
Greyscale equivalent#666666
Inverted#999999
Colour vision & accessibility
Distinguishable without hueYesnever rely on hue alone to carry meaning
Contrast with white, large text5.74:1WCAG large text: AAA
Contrast with black, large text3.66:1WCAG large text: AA
Named colours
Hue familygrey
CSS keyword usableNo exact keyword
Colour harmonies
Complementary#666666
Analogous#666666, #666666
Triadic#666666, #666666
Split complementary#666666, #666666
Tetradic#666666, #666666, #666666
Tints, shades & saturation
Channel breakdown
R102
G102
B102
Red102 (40%)
Green102 (40%)
Blue102 (40%)
Hue0°
Saturation (HSL)0%
Lightness40%
Dominant channelNone: the channels are equal (a neutral grey)
Hex per channelR 66 · G 66 · B 66
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Harmonies
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