There are 123456 six numbers in total. Every four numbers make up a group of numbers. At the same time, 6 can't be in thousand digits and 1 can't be in single digits. How many combinations are there? Except that 6 can't be in the thousand digits, all other digits are OK, just like 1. Hope to give the method

1、 A (6,4) = 6 * 5 * 4 * 3 = 360, 2,6 in the first place, a (5,3) = 5 * 4 * 3 = 601 in the last place, a (5,3) = 5 * 4 * 3 = 601 in the last place, a (5,3) = 60, 3,6 in the first place, 1 in the last place, and 2 in the remaining 5 numbers

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