Problem 012

[Prince_Mandor]

Problem 12 has a bad choice of words in body of question.
Example there says about 7th triangular number 28. And question is "Which is the first triangle number..."
For me it was a question about numerical order of this number (7 for example), not about number itself (28 in same example). In the header of this problem on a problems list wording is more correct ("What is the first triangle number..." )
This cause misunderstanding. Especially for foreigners, who translate it literally.

[euler]

That's an interesting question, Prince_Mandor. In English the subtle difference between "what" and "which" when used as an interrogative pronoun, as in this case, is to do with the number of choices. For example, "What would you like?" is an open question to which possibilities are almost endless, whereas, "Which would you like?" is a closed question that implies there is a limited choice.

So should it be?
"Which is the first triangle number to have over five-hundred divisors?"
or
"What is the first triangle number to have over five-hundred divisors?"

I'm not sure!?

But whichever way I think there is another problem with the wording in that I am not convinced whether it is clear that we are referring to the position or the size of the triangle number? For example, "What is the first triangle number to have over five divisors?" Is the answer 7 or 28?

[Prince_Mandor]

Sorry, I'm not native speaker, so I cannot help you here.
Just point you to the place of possible misunderstanding.

For me answer to 'What number?' is number itself, and answer to 'Which number?' must be guessed from context -- 'left one', '7th one', 'green one', 'first number in third string' etc...
Possibly just adding 'Note:' section to this problem will be enough.

[euler]

Sorry, I'm not native speaker, so I cannot help you here.

I am, and I can't help!

We'll see if anyone else has an insight into the correct usage.

[Helen]

I started working on Problem 12 yesterday, and couldn't tell which meaning was intended. But I don't think using "which" or "what" makes much difference here. I would say that the confusion arises from the line above: "We can see that the 7th triangle number, 28, is the first triangle number to have over five divisors." If, as I understand from this topic, 28 is the answer to the example question, then I think this could be resolved by changing that line to: "We can see that 28 is the first triangle number to have over five divisors."

[ed_r]

How about:

What is the value of the first triangle number to have over five hundred divisors?

Note also (while we're being picky) the absence of any hyphen in five hundred.

[euler]

Perfect! Thanks, Helen and ed_r.

[Tommy137]

"We can see that 28 is the first triangle number to have over five divisors."

Seems like a good solution to me. Everyone should know that 28 is the 7th triangle number

[Prince_Mandor]

How about:

What is the value of the first triangle number to have over five hundred divisors?

Note also (while we're being picky) the absence of any hyphen in five hundred.

Problem 25 has an opposite situation. Can you change the question of Problem 25 in similar way?

[ed_r]

Honestly, do you really think anyone's going to type in a 1000 digit answer to that question?

You could have ...

What is the index of the first term in the Fibonacci sequence to contain 1000 digits?

... I suppose; but then you'd need to define "index" elsewhere in the problem text. Surely it's just not worth the bother.

[hk]

I don't think it important to change it but reading the problem statement one could simply ask

What is the smallest value of n for which F_n has 1000 digits.

As everything is defined properly before that.

[ed_r]

Not quite properly: as currently stated, the answer to the problem should be negative!

[elendiastarman]

true, since the fibonacci sequence extends backwards
besides, such an answer would be negative infinity because F(-infinity) has more than 1000 digits and is the least value of n
surely, anyone with enough intelligence to solve this problem would use common sense and use the positive answer for n
so it doesn't really need to be changed...

[shorty_bobert]

What's the answer to problem 12 anyone?

[Georg]

The first triangle number having over five-hundred divisors.

[daniel.is.fischer]

In case that's the problem: the number, not the index.

[geek69]

I hope this isn't a duplicate post - I did a quick search and nothing turned up, but I find it hard to believe I'm the first person to have noticed this.

In the PDF for problem 12, snip, the third block of example code doesn't work. Within the while loop the cnt value doesn't get reset so as it gets multiplied by 2 twice within the loop it quickly reaches 512 and exits.

Simply adding cnt=1 in the while loop fixes the problem. For example:
...
array of int: primearray[1..P]
while cnt <= 500 {
cnt = 1
a = a+1
...

[pianowow]

Taking a look I see that a similar bug is in all three examples.

[harryh]

I had to snip the reference to the pdf, since not everyone reading this forum has solved the problem; leading them straight to a solution wouldnot be fair, would it?

I'm sure all the examples are correct, so I'm trying to guess what exactly is confusing you...
You need to count all the divisors, not just those that include a particular prime number. So, how can you reset the counter at each prime number you examine?

PS: Apologies, I see what you mean... Thanks for pointing it out. We'll fix it soon !

[geek69]

Oops! Sorry for posting the PDF - that wasn't very considerate of me. I'll know for next time.

Thanks for looking into it!