# 2, 5, 8, 11, 14... (continued)

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• February 12th 2006, 11:25 AM
Natasha
2, 5, 8, 11, 14... (q1)
Which cube members are not in the sequence and prove it?

2, 5, 8, 11, 14, ...

How can this be proved :confused:
• February 13th 2006, 01:48 PM
ThePerfectHacker
Quote:

Originally Posted by Natasha
Which cube members are not in the sequence and prove it?

2, 5, 8, 11, 14, ...

How can this be proved :confused:

Thus you want to find,
$3k+2=x^3$
I believe you may state that,
$x^3\equiv 1\mod 3$
if and only if, (there is a $k$ such as)
$3k+2=x^3$.
Thus, all the values of $x$ which are
"cubic residues" which are $1,4,7,10,13,...$
Maybe?