find the wrong term in the given series

63,28,215,511

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- May 24th 2008, 10:12 AMneha1find wrong term
find the wrong term in the given series

63,28,215,511 - May 24th 2008, 10:14 AMearboth
- May 24th 2008, 10:14 AMMoo
Hello,

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 :D

And another one :

- I don't know what term to choose, and I don't want to bother, so $\displaystyle \emptyset$ is the wrong term :p - May 24th 2008, 10:27 AMIsomorphism
- May 24th 2008, 10:43 AMearboth
- May 24th 2008, 09:02 PMIsomorphism
- May 25th 2008, 01:53 AMSoroban
Hello, hena!

Quote:

Find the wrong term in the given sequence: 63, 28, 215, 511

*cubes*. . . $\displaystyle 4^3 = 64,\quad 6^3 = 216,\quad 8^3 = 512$

We have: .$\displaystyle \begin{array}{cccc}

63 & 28 & 215 & 511 \\

\downarrow & \downarrow & \downarrow & \downarrow \\

4^3-1 & \quad{\color{red}?}\quad & 6^3-1 & 8^3-1 \end{array}$

The terms are of the form: $\displaystyle n^3-1$

. . except 28, which is $\displaystyle 3^3 {\color{red}+} 1$ . . . and is in the wrong position.

- May 25th 2008, 07:46 PMmr fantastic