MathDB
erasing some digits

Source: Indonesia IMO 2010 TST, Stage 1, Test 5, Problem 4

November 12, 2009
combinatorics proposedcombinatorics

Problem Statement

Prove that the number (9999…99⏟2005)2009 (\underbrace{9999 \dots 99}_{2005}) ^{2009} can be obtained by erasing some digits of (9999…99⏟2008)2009 (\underbrace{9999 \dots 99}_{2008}) ^{2009} (both in decimal representation). Yudi Satria, Jakarta
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