Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

No, I did not read it.

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

No, I did not read it.

Hahhahhaha, very good! Wunderbar!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

Where did Somos get those reccurences from?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

He is an expert in combinatorics and sequences. While I am an occasional contributor to the OEIS he is a major force. It is his knowledge of sequences that produces those. I know the technique but I lack the skill even with M. But as you should know RIPOSTP is allowed in problem solving.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,398

Define a function as follows:

n ∈ [3,6] f(n) = n + 3

n ∈ [9,18] f(n) = n + 9

n ∈ [27,54] f(n) = n + 27

in general:

n ∈ [3^k, 2 times 3^k] f(n) = n + 3^k

n ∈ (6,9) f(n) = n + 2n - 9

n ∈ (18,27) f(n) = n + 2n - 27

n ∈ (54,81) f9n) = n + 2n - 81

in general:

n ∈ (2 times 3^k, 3^(k+1)) f(n) = n + 2n - 3^(k+1)

f(2001) ?

As 1458 < 2001 < 2187 k = 6 and f(2001) = 2001 + (4002 - 2187) = 3816

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Agnishom wrote:

Where did Somos get those reccurences from?

They come from the additive solution to the Cauchy equation, see p6 of Introduction to Functional Equations by Prasanna K. Sahoo.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

Okay. Do you know why you revived this thread?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Some guy that has your username asked a question that I was unable to give a good answer to before. The book I was reading for another functional problem had a good answer.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

Much time has passed and some questions were not answered. I remedy that here.

Agnishom wrote:

your code, please?

```
a[n_] := 3 a[n/3] /; Mod[n, 3] == 0 && n > 1;
a[n_] := 2 a[(n - 1)/3] + a[(n - 1)/3 + 1] /; (Mod[n, 3] == 1 && n > 2);
a[n_] := a[(n - 2)/3] + 2 a[(n - 2)/3 + 1] /; (Mod[n, 3] == 2 && n > 3);
```

`a[2001] /. a[1] -> 2 /. a[2] -> 3`

3816

If you want to see M in action...

`a[2001] // FullSimplify`

Agnishom wrote:

What is J-rod?

A thing that exists in Nevada. Mind you I have never had access to this creature. It will only communicate with engineer types.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

Is J-rod a supercomputer?

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

Offline