5995

Number
$5995$ (five thousand, nine hundred and ninety-six) is:


 * $5 \times 11 \times 109$


 * The $11$th palindromic triangular number after $0$, $1$, $3$, $6$, $55$, $66$, $171$, $595$, $666$, $3003$


 * The $55$th hexagonal number after $1$, $6$, $15$, $28$, $45$, $66$, $91$, $\ldots$, $4005$, $4186$, $4371$, $4560$, $4950$, $5151$, $5356$, $5565$, $5778$:
 * $5995 = \displaystyle \sum_{k \mathop = 1}^{55} \paren {4 k - 3} = 55 \paren {2 \times 55 - 1}$


 * The $109$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $5253$, $5356$, $5460$, $5565$, $5671$, $5778$, $5886$:
 * $5995 = \displaystyle \sum_{k \mathop = 1}^{109} k = \dfrac {109 \times \paren {109 + 1} } 2$