Recognised as Number
991
- Positive
- Odd
- Prime
- 3 digits
991 is an odd 3-digit integer and a prime number. It has 2 divisors and a digital root of 1.
Number properties
ParityOddnot divisible by 2
SignPositive
PrimalityPrime
Absolute value991
Digit count3
Digit sum19
Digit product81
Multiplicative persistence2times the digit product can be taken before one digit is left
Digital root1repeated digit sum
PalindromicNoreads differently backwards
Happy numberNosquared-digit sums reach 1
Harshad numberNodivisible by its own digit sum
Factors & divisors
Prime factorisation991
Distinct prime factors1991
Number of divisors2
Sum of divisors σ(n)992
Aliquot sum1sum of the proper divisors
ClassificationDeficientthe aliquot sum is less than the number
Euler's totient φ(n)990integers below n that share no factor with it
Carmichael function λ(n)990the smallest exponent with aˣ ≡ 1 for every unit coprime to n
Möbius function μ(n)−11 distinct prime factor, an odd number of them
SquarefreeYesno repeated prime factor
All divisors1, 9912 in total
Arithmetic
Representations
Decimal991
Binary111101111110 bits
Octal1737
Hexadecimal3DF
Base 36RJ
Roman numeralCMXCI
In wordsnine hundred and ninety-one
Ordinalnine hundred and ninety-first
Scientific notation9.91 × 10^2
Engineering notation991
In other bases
Ternary1100201base 3; the most digit-efficient integer base after e: 7 digits
Quinary12431base 5; one hand: 5 digits
Septenary2614base 7: 4 digits
Nonary1321base 9; each digit is two ternary digits: 4 digits
Duodecimal6a7base 12; divides by 2, 3, 4 and 6, which is why eggs and inches come in twelves: 3 digits
Vigesimal29bbase 20; hands and feet, and the Mayan and Yoruba systems: 3 digits
Sexagesimal16:31base 60; Babylonian, and still how an hour and a circle are divided: 2 digits
Balanced ternary1101T01digits −1, 0 and +1 written T, 0 and 1; negation is swapping T and 1, so no sign is needed
Negabinary10000100011base −2; place values alternate 1, −2, 4, −8, so every integer has exactly one form without a sign
Bit-level
0000001111011111
Bit length10 bitsto write the magnitude
Set bits9the population count, or Hamming weight
Zero bits1within that length
Bit parityodd9 set bits, so odd; not the same as the number itself being odd
Highest set bitbit 9worth 512
Lowest set bitbit 00 trailing zeros
Power of twoNo
Bytes203 df
Gray code1000110000n XOR (n >> 1); successive values differ in exactly one bit
At each machine width
16-bit0000001111011111
32-bit00000000000000000000001111011111
64-bit0000000000000000000000000000000000000000000000000000001111011111
One's complement1111110000100000at 16 bits, every bit flipped
Bits reversed1111101111000000at 16 bits
Rotated left by 10000011110111110at 16 bits, wrapping
Shifted left by 111110111110= 1,982, no wrap
Shifted right by 1111101111= 495, discarding the low bit
These bits as a double4.89619055 × 10^-321≈IEEE-754 binary64 reinterpretation of the same 64 bits (subnormal)
Nearest landmarks
Powers & multiples
991 to the power 2982,081
991 to the power 3973,242,271
991 to the power 4964,483,090,561
991 to the power 5955,802,742,745,951
First ten multiples991, 1,982, 2,973, 3,964, 4,955, 5,946, 6,937, 7,928, 8,919, 9,910
Powers of twoBetween 2^9 (512) and 2^10 (1,024)
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 4
Divisible by 8No, remainder 7
Divisible by 9No, remainder 1
Divisible by 10No, remainder 1
Divisible by 11No, remainder 1
Divisible by 12No, remainder 7
Divisible by 100No, remainder 91
Collatz (3n + 1) trajectory
Steps to reach 198the total stopping time
Reaches 1Yesthe Collatz conjecture says every positive integer does, but it is unproven
First steps991 → 2,974 → 1,487 → 4,462 → 2,231 → 6,694 → 3,347 → 10,042 → 5,021 → 15,064 → …
Last steps… → 5 → 16 → 8 → 4 → 2 → 1
As a percentage & fraction
As a percentage99,100%
991% as a decimal9.91
991% of 100991
991% of 1,0009,910
As a fraction of 100991/100
Read another way
Keep nerding
Every link below is a page Nerdulator can generate from what it already knows about this value.
Derived from 991
Other readings
Also reads as
#999911 (colour)
- #999911
- Yellow
- Dark
- Nearest: Olive
#999911 is a yellow with RGB values 153, 153, 17 and HSL 60°, 80%, 33%. It is a dark colour, so black text on it reaches 6.9:1 contrast (AA for normal text). The nearest named colour is Olive.
Colour values
#999911#999911
HEX#999911
HEX (short)#991
RGBrgb(153, 153, 17)
RGB (0–1)0.6, 0.6, 0.0667
RGB percentages60%, 60%, 6.7%
HSLhsl(60, 80%, 33.3%)
HSV / HSBhsv(60, 88.9%, 60%)
CMYK0%, 0%, 88.9%, 40%≈naive device-independent conversion; real print needs an ICC profile
24-bit integer10,066,193
CSS custom property--colour: #999911;
Brightness & contrast
Relative luminance0.29595WCAG 2.x, 0 is black and 1 is white
Perceived brightness144.1 of 255ITU-R BT.601 weighting
Light or darkDark
Best text colour on this backgroundBlackcontrast 6.92:1
Contrast with white3.04:1WCAG normal text: Fail
Contrast with black6.92:1WCAG normal text: AA
Greyscale equivalent#8F8F8F
Inverted#6666EE
Colour vision & accessibility
Distinguishable without hueYesnever rely on hue alone to carry meaning
Contrast with white, large text3.04:1WCAG large text: AA
Contrast with black, large text6.92:1WCAG large text: AAA
Named colours
Hue familyyellow
CSS keyword usableNo exact keyword
Colour harmonies
Complementary#111199
Analogous#995511, #559911
Triadic#119999, #991199
Split complementary#115599, #551199
Tetradic#119955, #111199, #991155
Tints, shades & saturation
Channel breakdown
R153
G153
B17
Red153 (60%)
Green153 (60%)
Blue17 (6.7%)
Hue60°
Saturation (HSL)80%
Lightness33.33%
Dominant channelRed and Green
Hex per channelR 99 · G 99 · B 11
Keep nerding
Every link below is a page Nerdulator can generate from what it already knows about this value.
Nerdulate something else
Nothing in mind? Surprise me · today’s page