Problem 521

DeatH_StaR · Post by **DeatH_StaR** » Fri Jul 24, 2015 8:58 am

Hi all,
Can problem 521 be solved by the "one minute rule"?
Just *counting* to 10¹² 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?

TripleM · Post by **TripleM** » Fri Jul 24, 2015 9:31 am

Every problem satisfies the 1 minute rule. If you can't count to 10^12 in one minute, then clearly you shouldn't be trying to

DeatH_StaR · Post by **DeatH_StaR** » Fri Jul 24, 2015 10:20 am

Thanks, I got worried...

v6ph1 · Post by **v6ph1** » Sun Jul 26, 2015 12:55 am

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.

Marcus_Andrews · Post by **Marcus_Andrews** » Sun Jul 26, 2015 6:17 pm

DeatH_StaR wrote:Hi all,
Can problem 521 be solved by the "one minute rule"?
Just *counting* to 10¹² 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:

https://projecteuler.net/about

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.

vamsikal3 · Post by **vamsikal3** » Tue Nov 13, 2018 3:57 am

philiplu · Post by **philiplu** » Tue Nov 13, 2018 8:07 am

vamsikal3 wrote: Tue Nov 13, 2018 3:57 am Can someone verify the answer for n = 201820182018 is <snipped by moderator>? Thanks!

Those are the correct final 9 digits.

vamsikal3 · Post by **vamsikal3** » Tue Nov 13, 2018 9:50 am

kenbrooker · Post by **kenbrooker** » Wed Nov 14, 2018 3:17 am

Ahhh... Silly me... I thought --
"This forum is not meant to publish solutions."
"In particular don't post any ... results."

yourmaths · Post by **yourmaths** » Wed Nov 14, 2018 9:45 am

There are plenty of test solutions in these forums... maybe the rule needs to be clarified?

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