求救：有沒有好辦法?

來源: 於 2009-10-23 20:23:12 [舊帖] [給我悄悄話] 本文已被閱讀：次

Numbers 1 through 10 are written on a board. At any time, numbers a, b, c
may be replaced by (2(b + c) − a)/3, (2(c + a) − b)/3, (2(a + b) − c)/3.
Can a number greater than 20 eventually appear on the board?

Thanks