## 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!