Find all 10 digit numbers using each of the digits once, such that the first digits form a number divisible by (for ?
Enter your answer as the sum of all such possible.
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Even digits must be at even positions, which leaves only odd numbers in odd positions.
0 must be last, and so 5 must be in position 5.
Last but one digit can be anything: a number made with digits from 1 to 9 (all but 0) is always a multiple of 9. We don't have to check anything.
Numbers can only start with
123, 129, 147, 183, 189,
321, 324, 327, 369, 381, 387,
723, 729, 741, 783, 789,
921, 927, 963, 981, 987,
Adding a 4th number (2 and 6 are the only possibilites) and the digit 5:
12365, 12965, 14725, 14765, 18325, 18365, 18925, 18965
32165, 32465, 32765, 36925, 38125, 38165, 38725, 38765,
72365, 72965, 74125, 74165, 78325, 78365, 78925, 78965,
92165, 92765, 96325, 98125, 98165, 98725, 98765.
With 6th digit: if it was ending in 25, then it must be 258. If 65, it must be 654.
123654, 129654, 147258, 147654, 183258, 183654, 189258, 189654
321654, 324654, 327654, 369258, 381258, 381654, 387258, 387654,
723654, 729654, 741258, 741654, 783258, 783654, 789258, 789654,
921654, 927654, 963258, 981258, 981654, 987258, 987654.
7th digit, only two odd digits left and result must be a multiple of 7:
1296547, 1472583, 3216549, 3816547, 7296541, 7836549, 9216543, 9632581.
8th digit is the only even digit left and we check if the 3 last digits make a multiple of 8: 12965(478) - no, 14725(836) - no, 32165(498) - no, 38165(472) - yes ,
72965(418) - no, 78365(492) - no, 92165(438) - no, 96325(814) - no.
Only 3'816'547'290 is valid.