75

Number
$75$ (seventy-five) is:


 * $3 \times 5^2$


 * The $18$th lucky number:
 * $1, 3, 7, 9, 13, 15, 21, 25, 31, 33, 37, 43, 49, 51, 63, 67, 73, 75, \ldots$


 * The $6$th Keith number after $14, 19, 28, 47, 61$:
 * $7, 5, 12, 17, 29, 46, 75, \ldots$


 * The $1$st of the $2$nd pair of consecutive integers which both have $6$ divisors:
 * $\tau \left({75}\right) = \tau \left({76}\right) = 6$


 * With $48$, an element of the $1$st quasiamicable pair:
 * $\sigma \left({48}\right) = \sigma \left({75}\right) = 124 = 48 + 75 + 1$