# Sequence question

Gold Member
the next sries:6,10,14...62
62 is the tenth number in the series.
what is the fourth number?

my answer is 22 because the series is a multplication of 2 with a prime number starting from 3.
2*3,2*5,2*7,2*11...2*31

so? is my answer correct?

## Answers and Replies

pnaj
Your rule works ... so it must be correct!!

Have confidence.

Homework Helper
There exist an infinite number of sequences having the given values. Your rule works- that's all one can ask.

Gold Member
"There exist an infinite number of sequences having the given values."
can you show me the other sequences?

Guybrush Threepwood
Originally posted by loop quantum gravity
can you show me the other sequences?

how about the sequence made from the first ten numbers repeated periodically?

Gold Member
Originally posted by Guybrush Threepwood
how about the sequence made from the first ten numbers repeated periodically?
care to explain?

Guybrush Threepwood
2*3,2*5,2*7,2*11, ..., 2*31, 2*3,2*5,2*7,2*11, ..., 2*31, 2*3,2*5,2*7,2*11, ..., 2*31, 2*3,2*5,2*7,2*11, ..., 2*31, .......
and so on

Gold Member
but it doesnt solve for the fourth number in this sequence or the 14 24 etc.

Guybrush Threepwood
Originally posted by loop quantum gravity
but it doesnt solve for the fourth number in this sequence or the 14 24 etc.

why not?
the series begins as you said 6,10,14...62
the tenth number is 62, the fourth is 22...
you didn't specified anything about the 14th or 24th number.....
this is one of the infinite number of sequences HallsofIvy said (IMO)

pnaj
I think 'loop quantum gravity' just wants to know WHY there are infinitely many 'rules' that would produce a single sequence.

So, for a clear example, look at the sequence ...

2, 4, 6, 8, ...

Here are some 'rules' to describe it:

(a) {2n: n is a natural number}
(b) {2n/1: n is a natural number}
(c) {4n/2: n is a natural number}
etc.

Although there are infinitely many, all of them are just 'versions' of (a) and are NOT interesting or of any value.

Sometimes this is not the case, though, and two quite different 'rules' can produce the same sequence and both are 'interesting'.

Homework Helper
But there doesn't have to be a simple rule-

I can just declare the sequence to be 6,10,14, -300, pi, &sqrt;(2)
10000, 999, -1,62, 1, 2, 3, 4, 5,.... with the rest being the positive integers in order.

I had a professor who gave us the sequence 21, 19, 17, 15, 13, and challenged us to find the next number.

The next number in the sequence was 32! Those were the numbers of the bus stops on his way to work. (Between 13 and 32, the bus turned off the main street it had been on.

jeffceth
good point. I think Occam's Razor is the most relevant principle to this question. Granted, there are an infinite number of possible solutions, but chances are the most basic, logical answer is the most useful(though not of necessity the only right answer).

jeffceth

Gold Member
Originally posted by Guybrush Threepwood
why not?
the series begins as you said 6,10,14...62
the tenth number is 62, the fourth is 22...
you didn't specified anything about the 14th or 24th number.....
this is one of the infinite number of sequences HallsofIvy said (IMO)
but the rule is the same as i pointed out, multiplication of a prime number by two.
i thought that in a sequence there could be infinite patterns to it.

Guybrush Threepwood
Originally posted by loop quantum gravity
but the rule is the same as i pointed out, multiplication of a prime number by two.

no it's not because after your rule, the 11th number is 2*37 = 74 and after mine it's 6. they're 2 different series....

i thought that in a sequence there could be infinite patterns to it.

I don't quite understand this.
If you define a sequence as being 2*(succesive prime numbers) there's only one sequence.
But if you define a sequence as 6, 10, 14, ..., 62, .... there a a infinite number of sequences that match. If there's nothing more in the definition any sequence you find to match the 1st, 2nd, 3rd and 10th number as defined earlier is correct.