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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First I want to say I really love this site and the problems, and I appreciate all the work that goes into creating them. I am not trying to complain, but I think I have to say something about the wording of problem 377.
The directions state:
Find .
Give the last 9 digits as your answer.
The first instruction is impossible to follow on an ordinary computer. I don't think I'm spoiling the problem by saying that the sum must include repunit(1317), which is greater than 1.11111e8650415919381337933. Numbers in that range cannot be stored in a reasonable amount of memory.
The people who have solved this have all transformed those instructions into the much more feasible:
I agree with thundre, this looks and sounds like a task. And it's an impossible task (greetings from 2012 to those reading this in 2022 or later!)
Also, why don't you verify something like f(5)=[censored] or f(1313)=[censored] as you normally do?
No need to despair. Since you only solved 21 problems so far, just keep solving the earlier problems and build up your knowledge incrementally. Then you can revisit this problem.
whakamaru wrote:I deduce that there is a clever solution, involving math that I won't understand. "Brute force" would be ridiculous. I guess I'll never know.
I agree with thundre, this looks and sounds like a task. And it's an impossible task (greetings from 2012 to those reading this in 2022 or later!)
Well, to be serious , this was my first thought too, meanwhile I grasp, this is rather philosophical than linguistic problem. "Finding a number" means finding it in your imagination. A number is a "number", and not just a sequence of digits. You can represent it any way you (and maybe others) like. Think of Graham's number (n->3(^^n)3)^64(4). For the number in question there is some "simpler, but not shorter" representation for instance. Find the number of grains of rice on a chessboard. Be it 18446744073709551615, FFFFFFFFFFFFFFFF, 3*5*17*257*641*65537*6700417 or (2^^^2)^(2^^2)-(2^2)^(2-2), you can't pick them up anyway...
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, this was my first thought too, meanwhile I grasp, this is rather philosophical than linguistic problem. "Finding a number" means finding it in your imagination. A number is a "number", and not just a sequence of digits. You can represent it any way you (and maybe others) like. Think of Graham's number (n->3(^^n)3)^64(4). For the number in question there is some "simpler, but not shorter" representation for instance. Find the number of grains of rice on a chessboard. Be it 18446744073709551615, FFFFFFFFFFFFFFFF, 3*5*17*257*641*65537*6700417 or (2^^^2)^(2^^2)-(2^2)^(2-2), you can't pick them up anyway...