Multiples of 3 and 5

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

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sum = 3 * (1 + 999 / 3) * (999 / 3) / 2 + \
      5 * (1 + 999 / 5) * (999 / 5) / 2 - \
      15 * (1 + 999 / 15) * (999 / 15) / 2
print sum

3和5的倍数

如果我们列出所有小于10且为3或5的倍数的自然数,我们得到3,5,6和9。这些数的和是23。找出所有低于1000且为3或5倍数的和。