@ @QW@ @óïbÿa@‡ÉÜa@ú†bjà@ @ : A CD EB 6 . ) 7 [AMC10A 2010] ( . 10 [AMC10A 2008] ( ) .1 [AHMSE 1998] ( ) d1d2d3 = d5d6d7 d1d2d3 = d4d5d6 d1d2d3d4d5d6d7 ) x ) .di ∈ {0,1,2,…,9} [AIME 1993] ( 4000 ≤ x < 7000 ( (28 ) . 0,1,2,…,9 0