Fun With Shells

Can any shell aficionados on this list explain the following  
amusement (prompt represents the shell in use).  The first two  
results are boringly predictable.  Bash, however, knows how to keep  
you guessing.

csh> set N=055
csh> echo $N
055

sh> N=055
sh> echo $N
055

bash-2.00> let N=055
bash-2.00$ echo $N
45



el bid