210

Number
$210$ (two hundred and ten) is:


 * $2 \times 3 \times 5 \times 7$


 * The $4$th primorial, after $1, 2, 6, 30$ (counting $1$ as the zeroth):
 * $210 = 7 \# = 2 \times 3 \times 5 \times 7$
 * Hence the smallest positive integer with $4$ distinct prime factors.


 * The $20$th triangular number after $1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190$:
 * $210 = \displaystyle \sum_{k \mathop = 1}^{20} k = \dfrac {20 \times \left({20 + 1}\right)} 2$


 * The $12$th pentagonal number after $1, 5, 12, 22, 35, 51, 70, 92, 117, 145, 176$:
 * $210 = 1 + 4 + 7 + 10 + 13 + 16 + 19 + 22 + 25 + 28 + 31 + 34 = \dfrac {12 \left({3 \times 12 - 1}\right)} 2$


 * The $2$nd pentagonal number after $1$ which is also triangular:
 * $210 = \dfrac {12 \left({3 \times 12 - 1}\right)} 2 = \dfrac {20 \times \left({20 + 1}\right)} 2$


 * The $7$th pentatope number after $1, 5, 15, 35, 70, 126$:
 * $210 = 1 + 4 + 10 + 20 + 35 + 56 + 84 = \dfrac {7 \left({7 + 1}\right) \left({7 + 2}\right) \left({7 + 3}\right)} {24}$


 * The $27$th highly abundant number after $1, 2, 3, 4, 6, 8, 10, 12, 16, 18, 20, 24, 30, 36, 42, 48, 60, 72, 84, 90, 96, 108, 120, 144, 168, 180$:
 * $\sigma \left({210}\right) = 576$


 * The $12$th untouchable number after $2, 5, 52, 88, 96, 120, 124, 146, 162, 188, 206$.


 * The $13$th integer $n$ after $1, 3, 15, 30, 35, 56, 70, 78, 105, 140, 168, 190$ with the property that $\tau \left({n}\right) \mathrel \backslash \phi \left({n}\right) \mathrel \backslash \sigma \left({n}\right)$:
 * $\tau \left({210}\right) = 16$, $\phi \left({210}\right) = 48$, $\sigma \left({210}\right) = 576$


 * The $11$th number after $1, 3, 22, 66, 70, 81, 94, 115, 119, 170$ whose $\sigma$ value is square:


 * The largest integer which can be represented as the sum of two primes in the maximum number of ways.

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