Question 1210514
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For a positive integer n, let \tau(n) be the sum of the positive integer divisors of n.  
Find the number of values of n, where 1 \le n \le 25, such that \tau(n) = 1.
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<pre>
Among all positive integer numbers 'n', there is only one value 'n', for which 

    tau(n) = 1.



This exclusive positive integer  'n' is  n = 1.


For all other positive integer 'n',  tau(n)  is greater than 1, which is obvious.


Therefore, there is only one positive integer 'n', for which  tau(n) = 1.


This exclusive value of 'n'  is  n = 1.
</pre>

Solved, with detailed explanations.



This task isn't worth the shell of an eaten egg - so simple is it.