The Winter Olympics is also called the White Olympics．At this time，many colorful stamps are published to mark the great Games．The first stamps marking the opening came out on January 25th，1932 in the United States for the 3rd White Olympics. From then on，publishing stamps during the White Olympics became a rule.
    During the 4th Winter Olympic Games a group of stamps were published in Germany in November l936. The five Olympics rings were drawn on the front of the sportswear．It was the first time that the rings appeared on the stamps of the White Olympics．
    In the 1950s，the stamps of this kind became more colorful．When the White Olympics came，the host countries(主办国) as well as the non-host countries published stamps to mark those Games．China also published four stamps in February 1980 when the Chinese sportsmen began to take part in the White Olympics．
    Japan is the only Asian country that has ever held the White Olympics．Altogether 14,500 million stamps were sold to raise money for this sports meeting．
    Different kinds of sports were drawn on these small stamps．People can enjoy the beauty of the wonderful movements of some sportsmen.

安哥拉长毛兔最细的兔毛半径约为2.5×10^-6米，这个数用小数表示为（   ）

（Ⅰ）求证：数列{b_n}是等差数列，并求数列{a_n}的通项公式；

（Ⅱ）求数列{a_n}的前n项和S_n．

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如图是三个直立于水平面上的形状完全相同的几何体（下底面为圆面，单位：cm）．将它们拼成如图的新几何体，则该新几何体的体积为（　　） cm³．