1+2+3+4+5+6+7+8+9.+999+1000=? Column mode

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9. + 999 + 1000 solution, get: (1 + 1000) * 1000 / 2 = 500500, that is, (a1 + an) * n / 2 another solution is: 1 + 999 = 10002 + 998 = 1000.499 + 501 = 1000499 * 1000 = 499000, the last remaining 500 and 100049000 + 1500 = 500500

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