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In response to
"I was today years old when I realized that any number (unless a multiple of 7) divided by seven results in the same digit pattern"
by
znufrii
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I remember learning that multiples of 9 when you add their digits together = 9 -- (edited)
Posted by
Inigo (aka Inigo)
Oct 29 '21, 07:34
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9 X 1 = 9
9 X 2 = 18, 1 + 8 = 9
9 x 3 = 27, 2 + 7 = 9
9 x 11 = 99, 9 + 9 = 18, 1+ 8 = 9
etc...
The one I like it a lot is that you can count by squares by adding 2 to the difference of the two previous squares.
So 1 squared = 1, and 2 squared = 4. The difference between the two is 3. 3 + 2 = 5. So add 5 to 4 and you get 3 squared. Then add 7 to 9 to get the next square. Then 9 to get the next square. Then 11 for the next and so on.
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