2850

Number
$2850$ (two thousand, eight hundred and fifty) is:


 * $2 \times 3 \times 5^2 \times 19$


 * The $38$th hexagonal number after $1$, $6$, $15$, $28$, $45$, $66$, $91$, $\ldots$, $2145$, $2278$, $2415$, $2556$, $2701$:
 * $2850 = \displaystyle \sum_{k \mathop = 1}^{38} \paren {4 k - 3} = 38 \paren {2 \times 38 - 1}$


 * The $75$th triangular number after $1$, $3$, $6$, $10$, $15$, $\ldots$, $2211$, $2278$, $2346$, $2415$, $2485$, $2556$, $2628$, $2701$, $2775$:
 * $2850 = \displaystyle \sum_{k \mathop = 1}^{75} k = \dfrac {75 \times \paren {75 + 1} } 2$