A place to air possible concerns or difficulties in understanding ProjectEuler problems. This forum is not meant to publish solutions. This forum is NOT meant to discuss solution methods or giving hints how a problem can be solved.

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Hi all,
Can problem 521 be solved by the "one minute rule"?
Just *counting* to 10^{12} took me on a fast computer more then 15 minutes (not finding primes, just counting).
So will I need to expect a slow solution, or am I missing something that will enable me to solve it fastly?

Even if you can not count from 1 to 10^12 within the 1 minute rule, it is possible to get the sum of all these numbers within less than 1 minute.
The same is true for some number theoretic functions.
So you may calc that sum in a different way.

-- v6ph1

PS: Simply sieving needs around 7 hours on a modern i7 CPU.

DeatH_StaR wrote:Hi all,
Can problem 521 be solved by the "one minute rule"?
Just *counting* to 10^{12} took me on a fast computer more then 15 minutes (not finding primes, just counting).
So will I need to expect a slow solution, or am I missing something that will enable me to solve it fastly?

We don't release problems unless we can confirm they are solvable in under a minute:

I've written my program but should it take days to get to the answer?
Absolutely not! Each problem has been designed according to a "one-minute rule", which means that although it may take several hours to design a successful algorithm with more difficult problems, an efficient implementation will allow a solution to be obtained on a modestly powered computer in less than one minute.