4095

Number
$4095$ (four thousand and ninety-five) is:
 * $3^2 \times 5 \times 7 \times 13$


 * The $90$th triangular number:
 * $4095 = \displaystyle \sum_{k \mathop = 1}^{90} k = \dfrac {90 \left({91 + 1}\right)} 2$


 * The $5$th and last Ramanujan-Nagell number after $0$, $1$, $3$, $15$:
 * $4095 = 2^{12} - 1 = \dfrac {90 \left({91 + 1}\right)} 2$