120
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Number
$120$ (one hundred and twenty) is:
- $2^3 \times 3 \times 5$
- The $1$st triperfect number:
- $\map {\sigma_1} {120} = 360 = 3 \times 120$
- The $2$nd triangular number after $6$ which can be expressed as the product of $3$ consecutive integers:
- $120 = T_{15} = 4 \times 5 \times 6$
- The $2$nd after $24$ of the $3$ integers which can be expressed as the product of both $3$ and $4$ consecutive integers:
- $120 = 4 \times 5 \times 6 = 2 \times 3 \times 4 \times 5$
- The $3$rd after $1$, $10$ of the $5$ tetrahedral numbers which are also triangular.
- The $4$th and final element of the Fermat set after $1$, $3$, $8$
- The $5$th factorial after $1$, $2$, $6$, $24$:
- $120 = 5! = 5 \times 4 \times 3 \times 2 \times 1$
- The $6$th untouchable number after $2$, $5$, $52$, $88$, $96$.
- The smallest positive integer greater than $1$ to appear $6$ times in Pascal's Triangle.
- The $6$th and last after $0$, $2$, $3$, $27$, $98$ of the integers which are the middle term of a sequence of $5$ consecutive integers whose cubes add up to a square
- $118^3 + 119^3 + 120^3 + 121^3 + 122^3 = 8 \, 643 \, 600 = 2940^2$
- The $8$th hexagonal number after $1$, $6$, $15$, $28$, $45$, $66$, $91$:
- $120 = 1 + 5 + 9 + 13 + 17 + 21 + 25 + 29 = 8 \paren {2 \times 8 - 1}$
- The $8$th tetrahedral number, after $1$, $4$, $10$, $20$, $35$, $56$, $84$:
- $120 = 1 + 3 + 6 + 10 + 15 + 21 + 28 + 36 = \dfrac {8 \paren {8 + 1} \paren {8 + 2} } 6$
- The $10$th highly composite number after $1$, $2$, $4$, $6$, $12$, $24$, $36$, $48$, $60$:
- $\map {\sigma_0} {120} = 16$
- The $10$th superabundant number after $1$, $2$, $4$, $6$, $12$, $24$, $36$, $48$, $60$:
- $\dfrac {\map {\sigma_1} {120} } {120} = \dfrac {360} {120} = 3$
- The smallest positive integer which can be expressed as the sum of $2$ odd primes in $12$ ways.
- The $15$th triangular number after $1$, $3$, $6$, $10$, $15$, $21$, $28$, $36$, $45$, $55$, $66$, $78$, $91$, $105$:
- $120 = \ds \sum_{k \mathop = 1}^{15} k = \dfrac {15 \times \paren {15 + 1} } 2$
- There are $17$ positive integers which have an Euler $\phi$ value $120$.
- The $23$rd highly abundant number after $1$, $2$, $3$, $4$, $6$, $8$, $10$, $12$, $16$, $18$, $20$, $24$, $30$, $36$, $42$, $48$, $60$, $72$, $84$, $90$, $96$, $108$:
- $\map {\sigma_1} {120} = 360$
- The $56$th (strictly) positive integer after $1$, $2$, $3$, $\ldots$, $95$, $96$, $102$, $108$, $114$, $119$ which cannot be expressed as the sum of distinct primes of the form $6 n - 1$
Arithmetic Functions on $120$
\(\ds \map {\sigma_0} { 120 }\) | \(=\) | \(\ds 16\) | $\sigma_0$ of $120$ | |||||||||||
\(\ds \map {\sigma_1} { 120 }\) | \(=\) | \(\ds 360\) | $\sigma_1$ of $120$ |
Also see
- Previous ... Next: Factorial
- Previous ... Next: Integers Representable as Product of both 3 and 4 Consecutive Integers
- Previous ... Next: Hexagonal Number
Historical Note
The number $120$ was at one time sometimes referred to in England as a long hundred.
Hence the use of the term short hundred for the number $100$.
Both terms are now obsolete in England, although the term great hundred for $120$ is still used in Germany and Scandinavia.
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $120$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $120$
Categories:
- Factorials/Examples
- Highly Composite Numbers/Examples
- Superabundant Numbers/Examples
- Tetrahedral Numbers/Examples
- Hexagonal Numbers/Examples
- Untouchable Numbers/Examples
- Triangular Numbers/Examples
- Highly Abundant Numbers/Examples
- Integers not Expressible as Sum of Distinct Primes of form 6n-1/Examples
- Triperfect Numbers/Examples
- Specific Numbers
- 120