jmc

We see that the largest power of 5 that is less than 1357 is $5^4=625$, and the largest multiple of 625 less than 1357 is 1250, or $2\cdot 625$. From here, we find that the largest power of five less than $1357-1250=107$ is $5^2=25$, and the largest multiple of 25 less than 107 is 100, or $4\cdot 25$. Next, the largest power of five that is less than $107-100=7$ is $5^1=5$, simply giving us 5 or $1\cdot 5$ as the largest multiple of 5. Finally, this leaves us with $7-5=2$, or $2\cdot 1=2\cdot 5^0$. Therefore, we can express 1357 as $2\cdot 5^4+0\cdot 5^3+4\cdot 5^2+1\cdot 5^1+2\cdot 5^0$, which gives us $\boxed{20412_5}$.