Determine the probability that for a positive base ten integer N drawn at random between 2 and 201 inclusively, the number N3 - 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.
The number n^3-1 must be of the form a^3 *b *(2*b-1) to enable
the sequence a,a(1+b),a(1+2*b)
e.g. a=2 b=6 gives us 8*7*13=728=3^9-1
and the 1st solution is 2,14,26 and if n were limited to first 9 integers the requested probability would be 1/9.
To continue- Write a program to find what pairs (a,b) create n^3-1:.
range until reaching 202^3.
-Then calculate probability
Edited on June 1, 2010, 12:42 am