Guy, Richard K., Unsolved problems in number theory. Third edition, Problem Books in Mathematics, Springer, New York (2004), xviii+437 pp.; section C9 "Packing sums of pairs", printed p. 177: the Erdős--Turán conjecture that f(n)>0 for all large n forces limsupf(n)=∞, with the prize offer. Library home: Guy 2004.