C. Williams, B. Thwaites, A. van der Poorten, W. Edwards,
and L. Williams,
Ulam's Conjecture continued again, 1000 pounds for proof.
Rumored proof disclaimed.
References, PPC Calculator J.,
9 (Sept. 1982) 23--24.
Gives some history of the problem.
B. Thwaites states he originated the problem in 1952 and offers
1000 pounds for a proof of the Conjecture.