Let n and k be positive integers with k ≤ n. From an n × n array of dots, a k × k array of dots is selected.The figure above shows two examples where the selected k × k array is enclosed in a square. How many pairs (n, k) are possible so that exactly 48 of the dots in the n × n array are NOT in the selected k × k array?
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n2-k2=48 -> (n+k)(n-k)=48 ->(2x+y)y=48,y比为偶数->48分解偶数组合为2x24,4x12,8x6三组
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