(1)1,2, 4, 8, (16), (32), 64 ... Rule: multiply by 2 in turn.

(2) 1, 3,7,15, (31), (63),127 ... Law: What is the square of 2 minus1?

(3)1,4, 9,16, (25), (36), 49 ... Law: What is the first term?

Fill in the blanks.

(1) With 7, 3 and 8, you can put out (6, 738, 783, 378, 387, 873 and 837) different three digits.

(2) Use 2, 0, 5, (205, 250, 502, 520 * * 4) to release the three different digits.

There are four table tennis players in class 6/kloc-0: Xiaoming, Xiaojun, Xiaogang and Xiao Yong. If two of them are selected to participate in the doubles competition, there are (6) different collocation schemes.

(4) After 5/7 is converted into decimal, the number at the 20th10 after the decimal point is (5).

Solution: Cycle every 6 digits after the decimal point (7 14285), 20 10÷6=335.

So it's five.