Problem 272

[ssp]

Hello,
i've found 63450979 numbers with C(n) = 242 and get wrong answer (3463044300794026317).
Is those numbers near to the right answer?

[zwuupeape]

There are about twice as many numbers

[viv_ban]

Somebody please confirm if the answer is 19543219365706 for n <= 3*10^8.
Thanks.

[zwuupeape]

No, but it's close - the first four digits are good

[viv_ban]

Thanks zwuupeape for reply. Can you please recheck the value because I am getting the same answer (for 3*10^8) with a completely different algorithm (semi brute force).

[zwuupeape]

Oh, you are correct. I have a pretty subtle bug there. My program misses exactly one number. I'm surprised it actually works for higher values, now that I think of it

So yeah, it's good. Sorry!

[viv_ban]

hey no problem!
I learned lot of new and interesting things and finally came up with faster and better algorithm.

[oleglyamin]

Could anyone confirm that:

1) there are 663 positive results for n <= 3 * 10^7 for a total of 13166591472.

2) there are 29454 positive results for n <= 3 * 10^8.

Thanks.

[oleglyamin]

Bump. See previous post.

EDIT: Solved.

[lld2006]

Could anyone confirm that:

1) there are 663 positive results for n <= 3 * 10^7 for a total of 13166591472.

2) there are 29454 positive results for n <= 3 * 10^8.

Thanks.

The result for 3e7 is not correct. It is really misleading.

[Jamie]

Could anyone confirm that:

1) there are 663 positive results for n <= 3 * 10^7 for a total of 13166591472.

2) there are 29454 positive results for n <= 3 * 10^8.

Thanks.

Strangely enough, I get these wrong results as well

EDIT: found my issue. Though I probably can't say too much about it.

[yourmaths]

Could anyone confirm that:

1) there are 663 positive results for n <= 3 * 10^7 for a total of 13166591472.

2) there are 29454 positive results for n <= 3 * 10^8.

Thanks.

Strangely enough, I get these wrong results as well

EDIT: found my issue. Though I probably can't say too much about it.

OK I have been working on and debugging this problem all day and finally got the "correct wrong" answer above - anyone who gets this far on the problem surely deserves partial credit.

[yourmaths]

For future solvers: if you end up getting the correct wrong answer above, you are about 95% there, and understand the problem well enough to identify the issue and solve it.

[mdean]

I think I'm getting close to solving this problem. So far, I have the one value in this thread that's been confirmed (by viv_ban and zwuupeape). I was wondering if I could pm someone who has completed this problem with my value for 3*10^9. If someone could confirm that this value is correct, it would help focus my troubleshooting. If this value is wrong, I could have larger issues, but at least I'd know where to start looking.

[MuthuVeerappanR]

Hi mdean,
If you could PM your value, I can confirm it.

[castrate]

I think I'm on the (seemingly)correct way, but the answer was wrong, even not the same with the "correct wrong" answer. Could you please check:
Is the smallest number satisfying C(n)=242 <snipped>?
And is the smallest number satisfying C(n)=242 and not divisible by 9 <snipped>?

Edit: Solved the problem.