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problem 28 · 9 lines

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<p>Starting with the number $1$ and moving to the right in a clockwise direction a $5$ by $5$ spiral is formed as follows:</p>
<p class="monospace center"><span class="red"><b>21</b></span> 22 23 24 <span class="red"><b>25</b></span><br/>
20  <span class="red"><b>7</b></span>  8  <span class="red"><b>9</b></span> 10<br/>
19  6  <span class="red"><b>1</b></span>  2 11<br/>
18  <span class="red"><b>5</b></span>  4  <span class="red"><b>3</b></span> 12<br/><span class="red"><b>17</b></span> 16 15 14 <span class="red"><b>13</b></span></p>
<p>It can be verified that the sum of the numbers on the diagonals is $101$.</p>
<p>What is the sum of the numbers on the diagonals in a $1001$ by $1001$ spiral formed in the same way?</p>
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