> Use Mathematica. The positive integers less than or equal 1000 that are not > prime but (2^n - n)/n is an integer are 1; 341 = 11*31; 561 = 3*11*17; and > ;645 = 3*5*43. The largest less than 10,000 is 8911 = 7*19*67. from what I remember, 1 is not considered a prime number.