13 + 115 + 135 + 163 +...+ 99.

13 + 115 + 135 + 163 +...+ 99.

13 + 115 + 135 + 163 +...+ 1999, = (1 - 13 + 13 - 15 + 15 - 17 +...+ 199 - 101) × 12, = (1 - 1101) × 12, = 100101 × 12, = 50101.