Four of the following five are alike in a certain way and so form a group. Which is the one that does not belong to that group?
Options:
A . 143
B . 63
C . 195
D . 15
E . 257
Answer: Option E
The given numbers can be written as follows : 143 = 122-1 ; 63 = 82-1 ; 195 = 142-1 ; 15 = 42-1 ; But, 257 = 162+1 Obviously, except 257, others can be written in the form of x2-1
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