The first digit would have to be 1, the remaining digits, zero.
111,111,111,111
100,000,000,000
1023456789
10234567
0123456789
10234567
Since there are only five different digits, a 6-digit number can only be generated if a digit can be repeated. If digits can be repeated, the smallest 6-digit number is 111111.
103
102
If repeated digits are allowed, then the largest 12-digit number is 999,999,999,999 .If repeated digits are not allowed, then the largest 12-digit number is 989,898,989,898 .If the same digit can't be used more than once, then the largest possible number has only10 digits. The number is 9,876,543,210 .
999,999,999,999
The smallest number with no digits repeated would either be zero or one, depending on the set of numbers you want to choose from.
1000000000 or, if negative numbers are permitted, then -9999999999