Hi
This will do it
NumberForm[Ceiling[1738517, 10^(IntegerLength[1738517] - 1)], {1, 2},
DigitBlock -> 3]
The Ceiling function is the one to get it to n significant digits like
In[9]:= Ceiling[1738517, 1000000]
Out[9]= 2000000
You will need some means of identifying how many digits are in the number before hand, easy enough if the actual number is a variable.
Hope that helps.
