2500

Number
$2500$ (two thousand, five hundred) is:


 * $2^2 \times 5^4$


 * The $50$th square number after $1$, $4$, $9$, $16$, $25$, $36$, $\ldots$, $1521$, $1600$, $1681$, $1764$, $1849$, $1936$, $2025$, $2116$, $2209$, $2304$, $2401$:
 * $2500 = 50 \times 50$


 * The $43$rd positive integer which cannot be expressed as the sum of a square and a prime:
 * $1$, $10$, $25$, $34$, $58$, $64$, $85$, $\ldots$, $1024$, $1089$, $1225$, $1255$, $1351$, $1414$, $1444$, $1521$, $1681$, $1849$, $1906$, $1936$, $2116$, $2209$, $2304$, $2500$, $\ldots$