See OEIS [A129818][1] and the unsigned version [A085478][2] as well as [A049310][3], [A011973][4], and [A054142][5].


  [1]: https://oeis.org/A129818
  [2]: https://oeis.org/A085478
  [3]: https://oeis.org/A049310
  [4]: https://oeis.org/A011973
  [5]: https://oeis.org/A054142