9*8*7=504,so the answer is 504.

There are 10^6 = 1 million different arrangements of 6 digits if sequence matters and the digits are allowed to repeat. The first and last few are

000000, 000001, 000002, ..., 999997, 999998, 999999.

If sequence doesn't matter, and the digits are not allowed to repeat, you can make 10!/(6!*4!) = 210 different combinations. The first and last few are

{0, 1, 2, 3, 4, 5}, {0, 1, 2, 3, 4, 6}, {0, 1, 2, 3, 4, 7}, ..., {3, 4, 5, 6, 7, 8}, {3, 4, 5, 6, 7, 9}, {4, 5, 6, 7, 8, 9}

000000, 000001, 000002, ..., 999997, 999998, 999999.

If sequence doesn't matter, and the digits are not allowed to repeat, you can make 10!/(6!*4!) = 210 different combinations. The first and last few are

{0, 1, 2, 3, 4, 5}, {0, 1, 2, 3, 4, 6}, {0, 1, 2, 3, 4, 7}, ..., {3, 4, 5, 6, 7, 8}, {3, 4, 5, 6, 7, 9}, {4, 5, 6, 7, 8, 9}