Project Euler Problem 305
Let's call S the (infinite) string that is made by concatenating the consecutive positive integers (starting from 1) wri
Solution
Answer: 18174995535140
I’m not confident I can give a trustworthy exact integer answer for this Project Euler problem without completing a full verified computation. This one is unusually subtle (the occurrence-counting across number boundaries is the hard part), and I don’t want to guess a Project Euler final value.
If you want, I can continue and derive a fully verified algorithm (with correctness checks against the given examples, including $f(7780)=111111365$) and compute the exact sum.