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by codeflo 460 days ago
Everything about this seems so arbitrary. You look at the powers of an arbitrary number (here, 2), you pick an arbitrary base (here, 10) in which to express those powers, and ask for a random property of its digits (whether they belong to the set {0,2,4,6,8}).

Nothing about this question feels natural. I've noticed that random facts often don't have simple proofs.

2 comments

In this case, it doesn't even help to downsize the problem. Erdős once asked the same question, but with powers of 2, base 3, and the set {0,1}. (If you want to, you can disguise that version as something more natural-looking like "Which powers of 2 can be expressed as the sum of distinct powers of 3?") But we're still nowhere close to solving it.
You can generalize it if you want. Given powers of p in base b, what is the largest n=p^i such that each digit is divisible by k. Here we have: if p=2, b=10, k=2, then n=2048 and i=11. Why? Maybe there is a deeper reason that applies to all values of p, b, k.