Having turned 26367 days old today, I noticed that this number is a member of OEIS A289364:
A289364 | Numbers n such that ϕ(x)=12×n+2 is solvable, where ϕ is Euler's totient. |
Up to 26367, the members of this sequence are:
0, 9, 42, 180, 285, 414, 567, 945, 1109, 1419, 2310, 2655, 3024, 4275, 4740, 5229, 5742, 8034, 10005, 10710, 12192, 14595, 15444, 16317, 18135, 19080, 20049, 21042, 22306, 26367
Clearly, the numbers x satisfying this equation are not numerous. However, I thought so what? Well, fortunately a link provided in the OEIS entry comments shed some light on the matter. I've taken a screenshot of the relevant part of the paper and this is shown in Figure 1.
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Figure 1 |
So it turns out that ϕ(x)=k does not have many solutions if n≡2mod12 and those solutions appear in OEIS A289364. Moreover, Carmichael's conjecture states that the equation is never uniquely satisfied for any positive integer k. This was certainly the case when I checked it out for 26367:if ϕ(x)=2×26367+2x=316969 or 633938The paper delves into why there are so few solutions when n≡2mod12 but I've not gone into that here. Perhaps I can cover that in a later post.
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