總是平方數. 12 + 22 + 22 = 9 = 3 2. 22 + 32 + 62 = 49 = 7 2 32 + 42 + 122 =169 = 13 2 42 + 52 + 202 = 441 = 21 2. 顯然,左式是n2+(n+1)2+[n(n+1)]2, n是自然數 ...
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