If repeats are allowed than an infinite number of combinations is possible.
2469135780
1.52415788 × 1018
1234567890-1234567856 = 34
You can make 5 combinations of 1 number, 10 combinations of 2 numbers, 10 combinations of 3 numbers, 5 combinations of 4 numbers, and 1 combinations of 5 number. 31 in all.
If repeats are allowed than an infinite number of combinations is possible.
If there are no restrictions on the 'combinations' then there are ten choices for the first digit and ten for the second: 10 x 10. (This implies possibilities such as 22 and 77.) If the digits must be different in each combination then the number of combinations taking two at a time from ten is C(10,2) = 10!/( 2! ( 10 - 2 )! ) = 45.
1234567890
2469135780
zero
1.52415788 × 1018
1234567890-1234567856 = 34
1 plus 1234567890 is 1234567891
You can make 5 combinations of 1 number, 10 combinations of 2 numbers, 10 combinations of 3 numbers, 5 combinations of 4 numbers, and 1 combinations of 5 number. 31 in all.
They are all single digit numbers.
1234567890+9876543210=11,111,111,100
1234567890 + 1098765432 = 2333333322