1, 1, 2, 3, 5...

Why is this not a fibonacci sequence and what are therefore the next two terms ?

Answers in a spoiler please.

Edited Tuesday at 12:13 AM2 days by studiot

It was for a different sequence, before the OP edit, so I deleted it.

Edited Tuesday at 12:16 AM2 days by Genady

I have a different answer, though I see I miswrote the sequence.

Abject Apologies, I can still change it.

9, 18

Edited Tuesday at 12:15 AM2 days by studiot

8 hours ago, studiot said:

1, 1, 2, 3, 5...

Why is this not a fibonacci sequence

You're asking, why it is not a Fibonacci sequence, but it looks like a Fibonacci sequence to me.

1 hour ago, Genady said:

You're asking, why it is not a Fibonacci sequence, but it looks like a Fibonacci sequence to me.

If it were fibonacci the next two numbers would be 8 and 13, swince 8 = 5 + 3 and 13 = 8 + 5

Just now, studiot said:

If it were fibonacci the next two numbers would be 8 and 13, swince 8 = 5 + 3 and 13 = 8 + 5

Yes, but we're not given the next two numbers, so we don't know that it is not fibonacci.

So what other sequence(s) start of like fibonacci but diverge from this pattern further down the line ?

This is an exercise in thinking out of the box.

1 minute ago, studiot said:

what other sequence(s) start of like fibonacci but diverge from this pattern further down the line ?

This is a different question, not the one in the OP.

2 minutes ago, studiot said:

This is an exercise in thinking out of the box.

I'm sorry you say this.

They are not random numbers, but in my opinion, too many authors especially popsci ones promote fibonacci as the sequence of Nature.

And this is Scienceforums not just Physicsforums or Mathforums.

It can be, e.g., [math]F_n=2F_{n-2}+F_{n-3}[/math].

44 minutes ago, Genady said:

It can be, e.g., [math]F_n=2F_{n-2}+F_{n-3}[/math].

How is this different from F_n = F_(n-1) + F_(n-2) ?

It still leads to the next two numbers being 8 and 13

Anyway, thank you for being the only member interested.

Think

Methane, ethane, propane, butane, pentane for 1, 1, 2, 3, 5

14 minutes ago, studiot said:

How is this different from F_n = F_(n-1) + F_(n-2) ?

You're right. They are equivalent.

20 minutes ago, studiot said:

Methane, ethane, propane, butane, pentane for 1, 1, 2, 3, 5

This is not a meaningful sequence; the order is arbitrary.

Edited Tuesday at 12:13 PM2 days by Genady

45 minutes ago, Genady said:

You're right. They are equivalent.

This is not a meaningful sequence; the order is arbitrary.

The sequence denotes the number of isomers of alkanes, in increasing order of the number of carbon atoms.

There is no known single formula for calculating this, but several methods in combinatorics and graph theory are available for high numbers which increase rapidly with carbon count.

It does however start off with the first five terms of the fibonacci as noted.

Edited Tuesday at 12:33 PM2 days by studiot

5 minutes ago, studiot said:

in increasing order of the number of carbon atoms

, for our convenience.

---

Another not Fibonacci:

328, 176, 105, 83, ...

What are the next terms?

Edited Tuesday at 12:59 PM2 days by Genady

Nature has no requirement for a mathematical formula to describe a sequence.

Any such is purely artificial, but is in accord with an ordering of the set of all alkanes.

However Nature does present us with conundrums involving sequences such as chicken and egg, non commutativity

3 minutes ago, studiot said:

Nature has no requirement for a mathematical formula to describe a sequence.

Any such is purely artificial, but is in accord with an ordering of the set of all alkanes.

However Nature does present us with conundrums involving sequences such as chicken and egg, non commutativity

And that's why the OP question is misleading.

IOW, a waste of time.

P.S. I should've guessed so as it is in The Lounge and not in The Puzzles.

18 minutes ago, Genady said:

IOW, a waste of time.

That is what lounges are for.

Thank you for the discussion anyway.

1 hour ago, studiot said:

The sequence denotes the number of isomers of alkanes, in increasing order of the number of carbon atoms.

Excuse me, but it is 1,1,1,2,3,5...

https://en.wikipedia.org/wiki/Alkane#Isomerism

2 hours ago, studiot said:

The sequence denotes the number of isomers of alkanes, in increasing order of the number of carbon atoms.

Your numbers show differences of connectivity, but not stereochemistry.

3 hours ago, Sensei said:

Excuse me, but it is 1,1,1,2,3,5...

https://en.wikipedia.org/wiki/Alkane#Isomerism

Yes you are quite right. Thank you +1

I shall have to check my sources more carefully.

Wisconsin professors of mathematics are are evidently unreliable.

2 hours ago, TheVat said:

Your numbers show differences of connectivity, but not stereochemistry.

No it can't be connectivity, though this plays a part in higher carbon counts as the maximum connectivity is 4 for an individual carbon atom.

This thread reminds me of the sequence: 1, 2, 4, 8, 16, ?