Question

Show that 7 is the only prime of form n^3-1

Answer 1

We know from the sum of a geometric sequence that for any \(x^n-1\), \(x-1\) divides it. Hence, if \(n \geq3\), then \(n^3-1\) is composite.

Answer 2

n^3 - 1 = (n-1)(n^2 + n + 1)

for n>2, n^3 - 1 isnot prime!!

Answer 3

That was quick....:-)

Answer 4

i got lucky for 10 problems!!

Answer 5

Let me think of another....