505

Number
$505$ (five hundred and five) is:


 * $5 \times 101$


 * The magic constant of a magic square of order $10$, after $1$, $(5)$, $15$, $34$, $65$, $111$, $175$, $260$, $369$:
 * $505 = \ds \dfrac 1 {10} \sum_{k \mathop = 1}^{10^2} k = \dfrac {10 \paren {10^2 + 1} } 2$


 * The $21$st positive integer $n$ after $0$, $1$, $5$, $25$, $29$, $41$, $49$, $61$, $65$, $85$, $89$, $101$, $125$, $145$, $149$, $245$, $265$, $365$, $385$, $485$ such that the Fibonacci number $F_n$ ends in $n$