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Old 07-27-2022, 03:28 PM
 
376 posts, read 189,566 times
Reputation: 221

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Contain 2,4,6,8,0 either

The only cases are ones containing a product that ends in 5?

Example

193 has no digits with 2,4,6,8,0
715 also does
193 x 715 = 137,995 which also has no digits 2,4,6,8,0

Try ANY pair of 3 digits with all 1,3,5,7,9 numbers and you’ll see there’s at least 1 even-numbered digit in the multiplied product and the rare time there isn’t, 100% of those rare times it’s with a value of 5 in the 1’s digit


Which means the highest pair that doesn’t have this property seems to occur when one of the 2 numbers multiplied together is less than 10.

Example: 7 X 53 = 371

9 X 13 = 117

Once both numbers have at least 2 digits I don’t think you can preserve excluding 2,4,6,8,0 without using a multiple of 5
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Old 07-28-2022, 05:37 AM
 
Location: Shawnee-on-Delaware, PA
6,518 posts, read 5,724,871 times
Reputation: 13063
Sounds boring. What's the prize?
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Old 07-28-2022, 07:23 AM
 
376 posts, read 189,566 times
Reputation: 221
I just want to know what prevents the alignment of odd digits with multiples all odd without a 5
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Old 07-28-2022, 07:45 AM
 
Location: Shawnee-on-Delaware, PA
6,518 posts, read 5,724,871 times
Reputation: 13063
OK good luck. I have a touch of the 'tism myself but I can't help you with that.
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Old 08-27-2022, 02:08 PM
 
Location: Planet Earth
39 posts, read 10,836 times
Reputation: 61
I don't know yet what prevents it but I tried 713 x 193 and got 137,609. Neither of the numbers that I multiplied has an even digit or a 5 and the answer has one even number (the 6). I've known about another mathematical phenomenon for years that I have never really spoken about. It is when you take any number and multiply it by itself. Then take the two numbers that are one more and less than the original number and multiply those. The end result is that the number multiplied by itself is one more than the other total. Examples: 2 x 2 = 4 which is one more than 3. 1 x 3 = 3. 5 x 5 = 25 which is one more than 24. 4 x 6 = 24.

Last edited by Pineapple674; 08-27-2022 at 02:10 PM.. Reason: Spelling error
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