# Le Monde puzzle [#1139]

April 23, 2020
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Want to share your content on R-bloggers? click here if you have a blog, or here if you don't. A weekly Monde current mathematical puzzle that reminded me of an earlier one (but was too lazy to check):

The integer n=36 enjoys the property that all the differences between its ordered divisors are also divisors of 36. Find the only 18≤m≤100 that enjoys this property such that all its prime dividers areof multiplicity one. Are there other such m’s?

The run of a brute force R search return 42 as the solution (codegolf welcomed!)

```y=z=1:1e5
for(x in y)z[y==x]=!sum(x%%diff((1:x)[!x%%(1:x)]))
y=y[z==1]
for(k in generate_primes(2,max(y)))y=y[!!y%%k^2]
```

where generate_primes is a primes R function. Increasing the range of y’s to 10⁵ exhibits one further solution, 1806.

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