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I need to compute the quotient $\frac{n-1}{\sigma(n)-n}$ over the list say $\{9,25,49,81,121,169,...\}$ where $\sigma(.)$ is the classic sum of divisor function.

I tried to use the following codes but it did not work:

((n-1)/(DivisorSigma[1,n]-n))/@\{9,25,49,81,121,169,...\}

What must be the correct code so that I can compute the stated quotient over the given list. Thanks a lot.

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closed as off-topic by happy fish, Bob Hanlon, Kuba Mar 9 '17 at 6:45

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – happy fish, Bob Hanlon, Kuba
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ you need n to be # and & at the end of the function, like in your recent question 139430... $\endgroup$ – Kuba Mar 9 '17 at 6:43
  • $\begingroup$ See ref/Function and linked topics $\endgroup$ – Kuba Mar 9 '17 at 6:44
  • $\begingroup$ Thanks a lot for helping me. @Kuba $\endgroup$ – Jr Antalan Mar 9 '17 at 9:34
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What you have applied to the list is not a function. You can do either of the following:

(*1*)
((#-1)/(DivisorSigma[1,#]-#))&/@{9,25,49,81,121,169}
(*2*)
Function[n, ((n - 1)/(DivisorSigma[1, n] - n))] /@ {9, 25, 49, 81, 121, 169}
(*3*)
f[n_] := ((n - 1)/(DivisorSigma[1, n] - n));
f /@ {9, 25, 49, 81, 121, 169}
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