Some (many) problems from Project Euler are interesting.

This one for instance, which looks intimidating at first: https://projecteuler.net/problem=672

Try not to spoil answers. You can give general ideas or ask general questions, but no solution here please.

**Caution**: Project Euler is addictive

Addictive? Naaaaaah. I only just want to do just one more puzzle And then another, and then another... Just one more after that, and then I'll quit. Promise.

As for that particular numero 672, did you find "the" solution yet? Probably since you mention it being intimidating at first, thus possibly implying that it is easy, oh so easy ... in hindsight.

I tried to solve it the elegant way some time ago, and failed horribly.

At one point I got sidetracked by one of those

*"hey, I wonder if ... works"* ideas that a) did not work out and b) took up waaay too much time. So at a certain point I just had to take a break from it. I did however find a polynomial expansion for S(n) as a function of the digits d

_{i} of n. And also got the value of the given N as sequence of repeating digits in base 7. So last step is to tie those together, with a modulo step in the middle for the coefficients of that S(n) polynomial expansion.

There probably is an elegant solution involving H(10) and some clever inductive step, but by now I am invested in medium brute forcing it the algebraic way. If only to see if that will also work. Basically trying to see if I can get it to work with symbolic regression. Total overkill, but this sort of problem is a nice vehicle for trying out some stuff. Plus, there is a known solution, so that's always nice.