Number
721
- Positive
- Odd
- Composite
- 3 digits
721 is an odd 3-digit integer and a composite number. It has 4 divisors and a digital root of 1.
Number properties
ParityOddnot divisible by 2
SignPositive
PrimalityComposite
Absolute value721
Digit count3
Digit sum10
Digital root1repeated digit sum
PalindromicNoreads differently backwards
Happy numberNosquared-digit sums reach 1
Harshad numberNodivisible by its own digit sum
Factors & divisors
Prime factorisation7 × 103
Distinct prime factors27, 103
Number of divisors4
Sum of divisors σ(n)832
Aliquot sum111sum of the proper divisors
ClassificationDeficientthe aliquot sum is less than the number
Euler's totient φ(n)612integers below n that share no factor with it
SquarefreeYesno repeated prime factor
All divisors1, 7, 103, 7214 in total
Arithmetic
Representations
Decimal721
Binary101101000110 bits
Octal1321
Hexadecimal2D1
Base 36K1
Roman numeralDCCXXI
In wordsseven hundred and twenty-one
Ordinalseven hundred and twenty-first
Scientific notation7.21 × 10^2
Engineering notation721
Nearest landmarks
Powers & multiples
721 to the power 2519,841
721 to the power 3374,805,361
721 to the power 4270,234,665,281
721 to the power 5194,839,193,667,601
First ten multiples721, 1,442, 2,163, 2,884, 3,605, 4,326, 5,047, 5,768, 6,489, 7,210
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 1
Divisible by 5No, remainder 1
Divisible by 6No, remainder 1
Divisible by 7Yes
Divisible by 8No, remainder 1
Divisible by 9No, remainder 1
Divisible by 10No, remainder 1
Divisible by 11No, remainder 6
Divisible by 12No, remainder 1
Divisible by 100No, remainder 21
Collatz (3n + 1) trajectory
Steps to reach 146the total stopping time
Reaches 1Yesthe Collatz conjecture says every positive integer does, but it is unproven
First steps721 → 2,164 → 1,082 → 541 → 1,624 → 812 → 406 → 203 → 610 → 305 → …
Last steps… → 5 → 16 → 8 → 4 → 2 → 1
As a percentage & fraction
As a percentage72,100%
721% as a decimal7.21
721% of 100721
721% of 1,0007,210
As a fraction of 100721/100
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Derived from 721
Other readings
Also reads as
#772211 (colour)
- #772211
- Red
- Dark
- Nearest: Maroon
#772211 is a red with RGB values 119, 34, 17 and HSL 10°, 75%, 27%. It is a dark colour, so white text on it reaches 10.4:1 contrast (AAA for normal text). The nearest named colour is Maroon.
Colour values
#772211#772211
HEX#772211
HEX (short)#721
RGBrgb(119, 34, 17)
RGB (0–1)0.4667, 0.1333, 0.0667
RGB percentages46.7%, 13.3%, 6.7%
HSLhsl(10, 75%, 26.7%)
HSV / HSBhsv(10, 85.7%, 46.7%)
CMYK0%, 71.4%, 85.7%, 53.3%≈naive device-independent conversion; real print needs an ICC profile
24-bit integer7,807,505
CSS custom property--colour: #772211;
Brightness & contrast
Relative luminance0.05106WCAG 2.x, 0 is black and 1 is white
Perceived brightness70.3 of 255ITU-R BT.601 weighting
Light or darkDark
Best text colour on this backgroundWhitecontrast 10.39:1
Contrast with white10.39:1WCAG normal text: AAA
Contrast with black2.02:1WCAG normal text: Fail
Greyscale equivalent#333333
Inverted#88DDEE
Colour vision & accessibility
Distinguishable without hueShifts in lightness toonever rely on hue alone to carry meaning
Contrast with white, large text10.39:1WCAG large text: AAA
Contrast with black, large text2.02:1WCAG large text: Fail
Named colours
Hue familyred
CSS keyword usableNo exact keyword
Colour harmonies
Complementary#116677
Analogous#771133, #775511
Triadic#117722, #221177
Split complementary#117755, #113377
Tetradic#337711, #116677, #551177
Tints, shades & saturation
Channel breakdown
R119
G34
B17
Red119 (46.7%)
Green34 (13.3%)
Blue17 (6.7%)
Hue10°
Saturation (HSL)75%
Lightness26.67%
Dominant channelRed
Hex per channelR 77 · G 22 · B 11
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