## Problem 155

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Comments, questions and clarifications about PE problems.

### Problem 155

Can anybody please confirm me if the values D(4) = 15 and D(5) = 35 are correct.

thanks in advance.

thanks in advance.

### Re: problem 155

Yes, they are correct.

### Re: problem 155

Thanks Tommy. I really cannot understand the problem with my algorithm. Is D(10) = 2491.

### Re: problem 155

Unfortunately, it's wrong

### Re: problem 155

I don't get it either...

Is it wrong to think, that the only new capacitor combinations are the ones from the previous, with max number of capacitors, + a series and a paralel with a new 60 microfahrad capacitor?

ex

if we have 2 2 capacitor combinations, then there will be 4 extra in the next, and 8 extra in the next and so on?

I cannot imagine how else a combination would be made, but then my D(5) = 31, and i don't see where the 4 extra comes from

Is it wrong to think, that the only new capacitor combinations are the ones from the previous, with max number of capacitors, + a series and a paralel with a new 60 microfahrad capacitor?

ex

if we have 2 2 capacitor combinations, then there will be 4 extra in the next, and 8 extra in the next and so on?

I cannot imagine how else a combination would be made, but then my D(5) = 31, and i don't see where the 4 extra comes from

### Re: problem 155

Hint: 5 = 1+4 = 2+3Schwein wrote:I cannot imagine how else a combination would be made, but then my D(5) = 31, and i don't see where the 4 extra comes from

Remember also that we only care about the different values - some values can be made in several completely different ways, so that is another reason why it won't be a simple doubling sequence.

_{Jaap's Puzzle Page}

### Re: problem 155

I had the part covered, that some values might be equal(turned out none of them were, when i just added one in series, and one in paralel, for each combo), the only thing i don't understand, is why that does not give me all the different combinations makeable...

- Lord_Farin
**Posts:**239**Joined:**Wed Jul 01, 2009 9:43 am**Location:**Netherlands

### Re: problem 155

How about combining larger, 'composite' capacitors in series or parallel? (This is what hk meant above as well)Schwein wrote:the only thing i don't understand, is why that does not give me all the different combinations makeable...

Think about $1 = \frac1{1+1}+\frac1{1+1}$.

### Re: problem 155

Ahhhhh, thank you were much the both of you, I see now where my logic fails ^^

### Re: problem 155

It seems I can't get it right... I get the correct results for D(4) and D(5). Then D(6) = 76 and D(10) = 2147. Are these values correct?

### Re: problem 155

No.Erf_Erf wrote:It seems I can't get it right... I get the correct results for D(4) and D(5). Then D(6) = 76 and D(10) = 2147. Are these values correct?

### Re: problem 155

I just found the annoyingly trivial and almost invisible mistake in my code, and finally got the correct answer.

### Re: problem 155

Hi all,

Could I ask for two pieces of input here:

1) D(13) is a 5-digit figure starting with a 4 and ending in an even digit - is that correct?

2) I'm using float values in C and my suspicion is that my solutions turns out wrong because of a precision issue. I've tried (long) double but the result is no more convincing. Should I try to go for the alternative of defining and manipulating fractions (as Wodehouse would have said: I've just had a look at what my mind is doing, and it turns out: it boggles!) or should I rather look for something else - my choice of value for the capacitance for example.

Cheers,

Claude

Could I ask for two pieces of input here:

1) D(13) is a 5-digit figure starting with a 4 and ending in an even digit - is that correct?

2) I'm using float values in C and my suspicion is that my solutions turns out wrong because of a precision issue. I've tried (long) double but the result is no more convincing. Should I try to go for the alternative of defining and manipulating fractions (as Wodehouse would have said: I've just had a look at what my mind is doing, and it turns out: it boggles!) or should I rather look for something else - my choice of value for the capacitance for example.

Cheers,

Claude

### Re: problem 155

Claude,

to answer your first question:

D(13) is indeed a 5-digit figure but it starts with 3 and ends with an odd digit.

hth

Jochen

to answer your first question:

D(13) is indeed a 5-digit figure but it starts with 3 and ends with an odd digit.

hth

Jochen

### Re: problem 155

Right, back to the drawing board then ...

Thanks for getting back though!

Thanks for getting back though!

### Re: Problem 155

Right, got there in the end, although the program takes about 40 seconds to come up with the answer...

Thanks for the help again!

Claude

Thanks for the help again!

Claude