[Guest]

Determine the probability that for a positive base ten integer N drawn at random between 2 and 201 inclusively, the number N⁴ - 1 is expressible in the form p*q*r, where p, q and r are three distinct positive integers such that p, q and r (in this order) corresponds to three consecutive terms of an arithmetic progression.

Edited March 9, 2010 by K Sengupta

[superprismatic]

0.35

[superprismatic]

I just caught my mistake. In my previous post, I used the

number of distinct arithmetic progression triples instead

of the number of Ns. Some Ns have more than one progression

associated with them. So,

0.27 precisely

Edited March 9, 2010 by superprismatic

[superprismatic]

I had a mistake in my counting method. I calculate the probability now as 0.505. N can be 2 or any odd number from 3 to 199.

Edited March 16, 2010 by superprismatic