Add them up.
20, 21, 22, 24, 25, 26, 27, 28, 30
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The sum is 3640.
It is: 11+13+17+19+23+29 = 112
The sum of the five odd numbers between 10 and 20 is: sum = 5 x (11 + 19) / 2 = 75.
38
Because the sum of its proper divisors is less than 19.