Do u know chemaths

Chemistry Level 3

Find the next number in the series $1,1,1,2,3,5,9,18,35,75, \ldots$

The answer is 159.

8 solutions

Satyabrata Dash
Mar 5, 2016

This is a simple sequence of the number of structural isomers of the first ten alkanes.

So the answer will be the number of structural isomers of $C_{11}H_{24}$ i.e 159

Yash Singh
Mar 17, 2015

it is the numbers of isomers of increasing alkanes, simply it was a non conceptual series it is the cramming part of chemistry

No!!!! @yash singh you should check the comments made by me, in pranjal's solution,so without thinking u can't call anything NON CONCEPTUAL.

Mehul Chaturvedi - 6 years, 2 months ago

Chew-Seong Cheong
Apr 9, 2015

I googled too and got the list:

1, 1, 1, 1, 2, 3, 5, 9, 18, 35, 75, 159, 355, 802, 1858, 4347, 10359, 24894, 60523, 148284, 366319, 910726, 2278658, 5731580, 14490245, 36797588, 93839412, 240215803, 617105614, 1590507121, 4111846763, 10660307791, 27711253769

See here .

Pranav Kirsur
Mar 15, 2015

https://oeis.org/A000602

Yeah! I googled it too!

Nihar Mahajan - 6 years, 3 months ago

Pranjal Jain
Feb 25, 2015

That's simply the number of isomers of $n-$ membered alkane. Here is the list.

@Mehul Chaturvedi This was a nice idea for proposing a problem. But I think this is not worth posting as the number of isomers cannot be calculated and it's almost impossible to draw all the possible isomers of higher alkanes. As you might know, there is no mathematical function defined for generating number of isomers. You might have kept it to lower alkanes like, at most 8.

Pranjal Jain - 6 years, 3 months ago

@Pranjal Jain there is a mathematical formula/function to calculate number of isomers

Mehul Chaturvedi - 6 years, 3 months ago

I couldn't find a general formula. Can you type it here? Thanks @Mehul Chaturvedi

Pranjal Jain - 6 years, 3 months ago

@Pranjal Jain – actually that is taught in college @Pranjal Jain .And the fact is that I too couldn't understand that function it's quite complicated.

Mehul Chaturvedi - 6 years, 3 months ago

@Mehul Chaturvedi – -_- Oh, I won't be pursuing chemical engg. in IIT.

Pranjal Jain - 6 years, 3 months ago

@Pranjal Jain – this year u would be appearing for IIT?

Mehul Chaturvedi - 6 years, 3 months ago

@Mehul Chaturvedi – Yes...

Pranjal Jain - 6 years, 3 months ago

@Pranjal Jain – all d best

Mehul Chaturvedi - 6 years, 3 months ago

@Mehul Chaturvedi – Thanks

Pranjal Jain - 6 years, 3 months ago

@Mehul Chaturvedi – This was an easy question since I had memorised the first ten numbers , so I recognised it and looked up the 11th one !

A Former Brilliant Member - 6 years, 3 months ago

@A Former Brilliant Member – Seriously ? you have great capabilyty of memorising man ! But Just curious what inspire you to learn't isomers upto 10 ? I'am astonished, Is there any mathamatical approach to this problem ?

Deepanshu Gupta - 6 years, 3 months ago

@Deepanshu Gupta – Sorry for the late reply ! I had memorized it long ago in Class 11 when I wasn't sure if I could understand the concept of Isomerism .

I just love memorizing things like lists , phone numbers , roll numbers $\dots$ and the list is endless !!

As for a Mathematical Approach , I don't think so that there is one .

A Former Brilliant Member - 6 years, 2 months ago

@Pranjal Jain you may check it here

Mehul Chaturvedi - 6 years, 3 months ago

This doesn't seem like an algebra question to me. It is an interesting fact, but I'm not sure how likely it would be to find next term with algebra alone. Might just be a polynomial of degree ten.

Danny Whittaker - 6 years, 3 months ago

wow man ! How did you kill this ? I mean I can never imagine that these are isomers ..... Have you learnt some isomers ?

Even I know title is 'chemaths' , but still I can't imagine!

Deepanshu Gupta - 6 years, 3 months ago

I was having some so called research over isomers,just then the idea clicked in my rusty mind,and is presented in front of u.

Mehul Chaturvedi - 6 years, 2 months ago

Aryan Goyat
Jan 28, 2016

just click on view wiki option just below the answer tab and you get the ultimate hint.

Ken Ken
Apr 14, 2015

This is the number of isomers of membered alkane.

Tanishq Varshney
Mar 15, 2015

C15H32 has 4347 isomers