shell scripting

1. how to write shell script to display the following series:
1,2,3,4,10,5,6,7,8,2,6,9,10,11,12,42,13,14,15,16,58,17,18,19,20,74

2.how to write a shell script that accepts two file names.it should swap the contents of these two file i.e. contents of file 1 should go in file2 and contents of file2 should go in file1.

3.how print the multiplication of any number,it should display : enter a number
2

2*1=2
2*2=4
...
...
2*10=20