# Math Help - find wrong term

1. ## find wrong term

find the wrong term in the given series
63,28,215,511

2. Originally Posted by hena
find the wrong term in the given series
63,28,215,511
How about 28 because it is the only even number?

3. Hello,

Originally Posted by hena
find the wrong term in the given series
63,28,215,511
Well, there are many possibilities...

- the numbers are odd, so 28 is the wrong term
- the numbers are in an increasing order, so 28 is the wrong term
- the sum of the numbers is <10, so 28 is the wrong term
- the one I prefer : they are all multiples of 7, so 215 is the wrong term

And another one :
- I don't know what term to choose, and I don't want to bother, so $\emptyset$ is the wrong term

4. Originally Posted by hena
find the wrong term in the given series
63,28,215,511
Though I am pretty sure of my answer, I dont know why I am sure :P

The odd one out is 28 because the rest all are 1 short of a power of 2

5. Originally Posted by Isomorphism
Though I am pretty sure of my answer, I dont know why I am sure :P

The odd one out is 28 because the rest all are 1 short of a power of 2
Well, ähemm - isn't there is a slight difference between 215 and 255

6. Originally Posted by earboth
Well, ähemm - isn't there is a slight difference between 215 and 255

7. Hello, hena!

Find the wrong term in the given sequence: 63, 28, 215, 511
Think cubes . . . $4^3 = 64,\quad 6^3 = 216,\quad 8^3 = 512$

We have: . $\begin{array}{cccc}
63 & 28 & 215 & 511 \\
\downarrow & \downarrow & \downarrow & \downarrow \\
The terms are of the form: $n^3-1$
. . except 28, which is $3^3 {\color{red}+} 1$ . . . and is in the wrong position.