6400

Number
$6400$ (six thousand, four hundred) is:


 * $2^8 \times 5^2$


 * The $31$st square number after $1$, $4$, $36$, $121$, $144$, $256$, $\ldots$, $5184$, $5776$, $6084$ to be the $\sigma$ (sigma) value of some (strictly) positive integer:
 * $6400 = \map \sigma {3591} = \map \sigma {4179} = \map \sigma {4503} = \map \sigma {6169}$


 * The $80$th square number after $1$, $4$, $9$, $16$, $25$, $36$, $\ldots$, $5041$, $5184$, $5329$, $5476$, $5625$, $5776$, $5929$, $6084$, $6241$
 * $6400 = 80 \times 80$