sequence of $N$ (decimal) digits on a board
Source: All-Russian 2007
May 4, 2007
algorithmcombinatorics unsolvedcombinatorics
Problem Statement
Arutyun and Amayak show another effective trick. A spectator writes down on a board a sequence of (decimal) digits. Amayak closes two adjacent digits by a black disc. Then Arutyun comes and says both closed digits (and their order). For which minimal they may show such a trick?
K. Knop, O. Leontieva