<image>On February 23, 2006, the "Nantong Daily" published the per capita disposable income of urban residents in Nantong City from 2000 to 2005 (as shown in the figure).

Based on the information in the figure:
(1) Find the median of the per capita disposable income of urban residents in Nantong City;
(2) In which years did the per capita disposable income of urban residents in Nantong City increase by more than 1,000 yuan compared to the previous year?
(3) If, starting from 2006, the per capita disposable income of urban residents in Nantong City increases by a yuan every year compared to the previous year, then by the end of 2008 it will reach 18,000 yuan. Find the value of a.