nakib77 wrote:

Can you guys explain it little more.....

I don't know if this is the easiest way to explain .. but from the stem..

For any number n>0 => (n-1)(n+1) has to be a factor of either 2 or 3 or both (plug some random values.. say n =59 => (58)(60) =>2,3,6 factors or say n=26 =>(25)(27) => 3 is a factor)

1) 2 is not a factor of n, out example of 59 shows r will be 0 but [edited: should consider something greater than 24] n=27, (26)(28) r is not zero. Insuff

2) 3 say n=26, (25)(27) divided by 24 will give some remainder r but this value again varies for every even value of n you consider. Insuff.

1&2 ... picking numbers is easy (since it cannot be a multiple of 2,3 or 6) ... say 49.. i.e. (48)(50) => r=0, or n=121 (120)(122) => r=0. So r=0 now for all values on n which is not a multiple of 2,3,6.

May not be the best explanation...But hope that helps.

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-Vikram