二百五十五角形
255 = 16 2 − 1 = ( 16 + 1 ) ( 16 − 1 ) = ( 16 + 1 ) ( 4 + 1 ) ( 4 − 1 ) = ( 16 + 1 ) ( 4 + 1 ) ( 2 + 1 ) ( 2 − 1 ) = 17 ⋅ 5 ⋅ 3 {\displaystyle 255=16^{2}-1=(16+1)(16-1)=(16+1)(4+1)(4-1)=(16+1)(4+1)(2+1)(2-1)=17\cdot 5\cdot 3}