Problem 521
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Don't post any spoilers
Comments, questions and clarifications about PE problems.

 Posts: 13
 Joined: Sat Apr 19, 2014 4:09 pm
Problem 521
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?
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?
Re: Problem 521
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
Re: Problem 521
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.
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
 Administrator
 Posts: 1447
 Joined: Wed Nov 09, 2011 5:23 pm
Re: Problem 521
We don't release problems unless we can confirm they are solvable in under a minute: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?
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 "oneminute 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.
Re: Problem 521
Can someone verify the answer for n = 201820182018 is <snipped by modrator>? Thanks!
my friend key > 990813_OZPwQtCjkD6KlvxirOoTSZxccMFsuw1L
Re: Problem 521
Thanks for verifying the result. philiplu, are you <snipped by moderator>? This blog was helpful in solving PE problems.
my friend key > 990813_OZPwQtCjkD6KlvxirOoTSZxccMFsuw1L
 kenbrooker
 Posts: 113
 Joined: Mon Feb 19, 2018 3:05 am
 Location: Oregon, USA
Re: Problem 521
Ahhh... Silly me... I thought 
"This forum is not meant to publish solutions."
"In particular don't post any ... results."
"This forum is not meant to publish solutions."
"In particular don't post any ... results."
"Good Judgment comes from Experience;
Experience comes from Bad Judgment..."
Experience comes from Bad Judgment..."
Re: Problem 521
There are plenty of test solutions in these forums... maybe the rule needs to be clarified?
level = lambda number_solved: number_solved // 25