The obvious first step is to obtain the list of factors with `k f`.
This list will always be in sorted order, so if there are duplicates
they will be right next to each other. A suitable method is to compare
the list with a copy of itself shifted over by one.

1: [3, 7, 7, 7, 19] 2: [3, 7, 7, 7, 19] 2: [3, 7, 7, 7, 19, 0] . 1: [3, 7, 7, 7, 19, 0] 1: [0, 3, 7, 7, 7, 19] . . 19551 k f RET 0 | TAB 0 TAB |

1: [0, 0, 1, 1, 0, 0] 1: 2 1: 0 . . . V M a = V R + 0 a =

Note that we have to arrange for both vectors to have the same length so that the mapping operation works; no prime factor will ever be zero, so adding zeros on the left and right is safe. From then on the job is pretty straightforward.

Incidentally, Calc provides the @c{\dfn{M\"obius} $\mu$}
**Moebius mu** function which is
zero if and only if its argument is square-free. It would be a much
more convenient way to do the above test in practice.

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