The sum of all numbers between 1 and n = n*(n+1)/2
The sum of all numbers between 1 and 999 = 999*1000/2 = 499500
The sum of all numbers between 1 and 9999 = 9999*10000/2 = 49995000
So, the sum of all numbers between 1000 and 9999 = 49495500
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The sum is 22 times the sum of the three digits.
2222
Four different digits that sum to 6 are: 0, 1, 2 & 3. The largest odd number that can be made from these is: 3201.
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