Math problem

[Kevin9]

Here's a number pattern: -2 1 6 13 22 33. The pattern is that for example the amount of numbers between -2 and 1 are 3. 1 and 6 is 5. 6 and 13 is 7. So it goes 3 5 7 9 11 13 etc. I need to make a formula that will work out which number is next in the first sequence but I can't think of one that will work.

[rja211077]

well if you only need a formula to calculate the next number it's easy enough. if x = next number, l = the last number you already have and p = penultimate number you already have then x = 2l - p + 2. If, however, you're actually after a general formula to calculate the nth number in the sequence then it's harder and i'm still working on it.

[rja211077]

ok i've got it (with the help of Excel). The nth number in the sequence is n squared minus 3. simple as that.

[ukkid76]

How do you get the amount of numbers between 2 and 1 as 3?

[Andromeda]

ukkud - thats -2 (minus 2) and 1. difference there is 3.