n=7的解决方案:
-----------------------------------
1 +8 +27 +64 +125 +216 +343 = 784.
1 +8 +27 +64 +125 +216 -343 = 98.
1 +8 +27 -64 +125 -216 +343 = 224.
1 +8 +27 -64 +125 -216 -343 = -462.
1 +8 +27 -64 -125 +216 +343 = 406.
1 +8 +27 -64 -125 +216 -343 = -280.
1 +8 -27 -64 +125 +216 +343 = 602.
1 +8 -27 -64 +125 +216 -343 = -84.
1 -8 +27 +64 +125 -216 +343 = 336.
1 -8 +27 +64 +125 -216 -343 = -350.
1 -8 +27 +64 -125 +216 +343 = 518.
1 -8 +27 +64 -125 +216 -343 = -168.
1 -8 +27 -64 -125 -216 +343 = -42.
1 -8 +27 -64 -125 -216 -343 = -728.
1 -8 -27 +64 +125 +216 +343 = 714.
1 -8 -27 +64 +125 +216 -343 = 28.
1 -8 -27 -64 +125 -216 +343 = 154.
1 -8 -27 -64 +125 -216 -343 = -532.
1 -8 -27 -64 -125 +216 +343 = 336.
1 -8 -27 -64 -125 +216 -343 = -350.