Recognised as Number
7
- Positive
- Odd
- Prime
- 1 digit
7 is an odd 1-digit integer and a prime number. It has 2 divisors and a digital root of 7.
Number properties
ParityOddnot divisible by 2
SignPositive
PrimalityPrime
Absolute value7
Digit count1
Digit sum7
Digit product7
Digital root7repeated digit sum
PalindromicYesreads the same backwards
Happy numberYessquared-digit sums reach 1
Harshad numberYesdivisible by its own digit sum
Armstrong numberYesdigits raised to the digit count sum to itself
Factors & divisors
Prime factorisation7
Distinct prime factors17
Number of divisors2
Sum of divisors σ(n)8
Aliquot sum1sum of the proper divisors
ClassificationDeficientthe aliquot sum is less than the number
Euler's totient φ(n)6integers below n that share no factor with it
Carmichael function λ(n)6the 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, 72 in total
Arithmetic
Representations
Decimal7
Binary1113 bits
Octal7
Hexadecimal7
Base 367
Roman numeralVII
In wordsseven
Ordinalseventh
Scientific notation7 × 10^0
Engineering notation7
In other bases
Ternary21base 3; the most digit-efficient integer base after e: 2 digits
Quinary12base 5; one hand: 2 digits
Septenary10base 7: 2 digits
Nonary7base 9; each digit is two ternary digits: 1 digit
Duodecimal7base 12; divides by 2, 3, 4 and 6, which is why eggs and inches come in twelves: 1 digit
Vigesimal7base 20; hands and feet, and the Mayan and Yoruba systems: 1 digit
Sexagesimal7base 60; Babylonian, and still how an hour and a circle are divided: 1 digit
Balanced ternary1T1digits −1, 0 and +1 written T, 0 and 1; negation is swapping T and 1, so no sign is needed
Negabinary11011base −2; place values alternate 1, −2, 4, −8, so every integer has exactly one form without a sign
Bit-level
00000111
Bit length3 bitsto write the magnitude
Set bits3the population count, or Hamming weight
Zero bits0within that length
Bit parityodd3 set bits, so odd; not the same as the number itself being odd
Highest set bitbit 2worth 4
Lowest set bitbit 00 trailing zeros
Power of twoNo
Bytes107
Gray code100n XOR (n >> 1); successive values differ in exactly one bit
At each machine width
8-bit00000111
16-bit0000000000000111
32-bit00000000000000000000000000000111
64-bit0000000000000000000000000000000000000000000000000000000000000111
One's complement11111000at 8 bits, every bit flipped
Bits reversed11100000at 8 bits
Rotated left by 100001110at 8 bits, wrapping
Shifted left by 11110= 14, no wrap
Shifted right by 111= 3, discarding the low bit
These bits as a double3.45845952 × 10^-323≈IEEE-754 binary64 reinterpretation of the same 64 bits (subnormal)
Nearest landmarks
Powers & multiples
7 to the power 249
7 to the power 3343
7 to the power 42,401
7 to the power 516,807
First ten multiples7, 14, 21, 28, 35, 42, 49, 56, 63, 70
Powers of twoBetween 2^2 (4) and 2^3 (8)
Divisibility tests
Divisible by 2No, remainder 1
Divisible by 3No, remainder 1
Divisible by 4No, remainder 3
Divisible by 5No, remainder 2
Divisible by 6No, remainder 1
Divisible by 7Yes
Divisible by 8No, remainder 7
Divisible by 9No, remainder 7
Divisible by 10No, remainder 7
Divisible by 11No, remainder 7
Divisible by 12No, remainder 7
Divisible by 100No, remainder 7
Collatz (3n + 1) trajectory
Steps to reach 116the total stopping time
Reaches 1Yesthe Collatz conjecture says every positive integer does, but it is unproven
First steps7 → 22 → 11 → 34 → 17 → 52 → 26 → 13 → 40 → 20 → …
Last steps… → 5 → 16 → 8 → 4 → 2 → 1
As a percentage & fraction
As a percentage700%
7% as a decimal0.07
7% of 1007
7% of 1,00070
As a fraction of 1007/100
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Derived from 7
Other readings
Also reads as
U+0037 (unicode character)
- U+0037
- 7
- Decimal digit
U+0037 is code point 55 (7), a decimal digit in the Basic Latin (ASCII) block of the Basic Multilingual Plane. It takes 1 byte in UTF-8 and 1 unit in UTF-16.
Identity
Code pointU+0037
Decimal55
Character7
General categoryDecimal digit
BlockBasic Latin (ASCII)
PlaneBasic Multilingual Planeplane 0
Official nameNot includedthe Unicode Character Database is not bundled; a stale copy would be worse than none
Encodings
UTF-8371 byte
UTF-160037a single unit
UTF-3200000037
Binary110111
Bytes in UTF-8 vs UTF-161 vs 2UTF-16 is not always smaller, even for non-Latin text
Writing it in code
HTML numeric entity7
HTML hex entity7
CSS escape\0037
JavaScript\u0037
Python\u0037
Percent-encoded (URL)%37
Things that catch people out
JavaScript string length1
Needs a surrogate pairNo
Safe in a URL unescapedYes
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