Guy, Richard K., Unsolved problems in number theory. 3rd ed., Problem Books in Mathematics, Springer, New York (2004), xviii+437 pp. Section A15 "Congruent products of consecutive numbers", printed p. 54, which records Erdős's example 3⋅4≡5⋅6⋅7≡1mod11, asks for the least prime with three congruent products, and reports the least primes found for several numbers of products. Library home: Guy 2004.