57/2=28..1
28/2=14..0
14/2=7..0
7/2=3..1
3/2=1..1
1/2=0..1
倒着把余数放一块即结果,为111001
验证：111001=1*2^5+1*2^4+1*2^3+0*2^2+0*2^1+1*2^0=32+16+8+0+0+1=57