[Guest]

Hello All!,

Ik was practicing sum number sequences for a school assignment on http://www.fibonicci.com/en/number-sequences

most are quite easy, but sum made my brain crack

1) 1 0 1 -1 2 ?

2) 34 -21 13 -8 5 ?

3) 1 3 7 11 13 ?

You know the answers?

[Guest]

1 0 1 -1 2 -3 5 -8 13

-1 +1 -2 +3 -5 +8 -13 +21 ...

Interesting how the sequence is just 1 number behind in the Fibonacci thing.

[Guest]

I don't know if it's this simple, but reverse Fibonacci Sequence with alternating negative signs. If the first 1 of the sequence equals x1, then it would go:

x9...-x8...x7...-x6...x5

[EventHorizon]

1. -3. fibonacci series backwards --- f(x+1) = f(x-1) - f(x)

2. -3. fibonacci series (forward...but starting in negatives) --- f(x+1) = f(x-1) + f(x)

[Guest]

Just learned about fibonacci last week. Didnt see a (reverse) negative fibonacci pew.

And ye funny to see how the first sequence and the answers are almost the same sequence like someguy said.

thx a lot, will beaware of a negative or reverse fibonacci next time heh!

And how about the 3rd sequence? It looks 2 easy, but just cant figure out for sure what to add to the last number +2 or +4?

? = 15 or 17?

[EventHorizon]

Just learned about fibonacci last week. Didnt see a (reverse) negative fibonacci pew.

And ye funny to see how the first sequence and the answers are almost the same sequence like someguy said.

thx a lot, will beaware of a negative or reverse fibonacci next time heh!

And how about the 3rd sequence? It looks 2 easy, but just cant figure out for sure what to add to the last number +2 or +4?

? = 15 or 17?

It could just be coincidence that the differences have been only 2's and 4's so far.

[Guest]

It could just be coincidence that the differences have been only 2's and 4's so far.

Yes, I was thinking that it was only a coincidence, but had to check the website given in the original post to see if there was a theme or rule to the type of sequences that they were asking about.

if you check out the site, even the answer is kind of ambiguous. Is the sequence, "add 2, 4, 4, 2, 4, 4..." or is it, "list the prime numbers that don't include 5's or 2's."?

(some people consider 1 to be prime)

[Guest]

Ye the sequence shows great simularity to the first prime numbers

2, 3, 5, 7, 11, 13, 17

The list dont include the 2's and the 5's, and should therefore not include 15? Which isnt a primenumber anyway.

Maybe it is to set people on the wrong foot and the sequence isnt about primenumbers.

If that was so, than it was a nice sequence. It gave me a "headache"

ps, havent figured out how to hide text in Spoiler. Sorry for this.

Edited October 19, 2008 by pE7e