2+4+6+8+10........+40=420
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110
The sum of the first 20 even numbers... is 110
int i, sum = 0; for (i=0; i<20; i+=2) sum+=i;
The sum of the squares of the first 20 natural numbers 1 to 20 is 2,870.
To find the sum of all even numbers between 10 and 20, we first need to identify the even numbers in that range. The even numbers between 10 and 20 are 10, 12, 14, 16, and 18. Adding these numbers together, we get 10 + 12 + 14 + 16 + 18 = 70. Therefore, the sum of all even numbers between 10 and 20 is 70.