99

Number
$99$ (ninety-nine) is:


 * $3^2 \times 11$


 * The $2$nd of the $3$rd pair of consecutive integers which both have $6$ divisors:
 * $\map {\sigma_0} {98} = \map {\sigma_0} {99} = 6$


 * The $5$th Kaprekar number after $1$, $9$, $45$, $55$:
 * $99^2 = 9801 \to 98 + 01 = 99$


 * The $6$th palindromic lucky number:
 * $1$, $3$, $7$, $9$, $33$, $99$, $\ldots$


 * The $8$th integer after $0$, $1$, $3$, $5$, $7$, $9$, $33$ which is palindromic in both decimal and binary:
 * $99_{10} = 1 \, 100 \, 011_2$


 * The $12$th trimorphic number after $1$, $4$, $5$, $6$, $9$, $24$, $25$, $49$, $51$, $75$, $76$:
 * $99^3 = 970 \, 2 \mathbf {99}$


 * The $22$nd lucky number:
 * $1$, $3$, $7$, $9$, $13$, $15$, $21$, $25$, $31$, $33$, $37$, $43$, $49$, $51$, $63$, $67$, $73$, $75$, $79$, $87$, $93$, $99$, $\ldots$

Also see