Find the sum of all even integers from 25 to 427.
The first even integer is 26
The last is 426
The number of terms = (426 - 26) / 2 + 1 = 200 + 1 = 201
The sum is
[ 26 + 426 ] (201/2) =
[ 452 ] / 2 * 201 =
45426