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Two numbers between 150 and 200 can each be expressed as the sum of two squares in two different ways.
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Make the table of squares of natural numbers between 0 and 200 (not so many opportunities)
0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196.
Make the table of sums of squares between 150 and 200 (not so many opportunities)
100 + 64 = 164
121 + 25 = 146
121 + 36 = 157
121 + 49 = 170
121 + 64 = 185 (**)
121 + 81 = 202
144 + 25 = 169 (*)
144 + 36 = 180
144 + 49 = 193
169 + 0 = 169 (*)
169 + 9 = 178
169 + 16 = 185 (**)
169 + 25 = 194
196 + 0 = 196
The repeating sums in this list are
169 = 169 + 0 = 144 + 25 (marked * in the list),
and
185 = 121 + 64 = 169 + 16 (marked ** in the list).
So, these two numbers, 169 and 185 are those you are looking for.
Their difference is 185 - 169 = 16. ANSWER
Solved.