Finding sum of a series of odd numbers

For numbers 1-5, find the nth term.

1. 28, 45, 66, 91, 120
2. 7, 24, 45, 70, 99
3. 15, 21, 28, 36, 45
4. 5, 28/3, 15, 22, 91/3
5. -2, 7/2, 15, 65/2, 56
6. Find the sum of the first 40 odd numbers.
7. Find the sum of the first 121 odd numbers.
8. Find the sum of the first 343 odd numbers.
9. 1+3+5+7+...+79=?
10. 1+3+5+7+...+241=?
11. 1+3+5+7+...+685=?
12. Given that the sum of the first 50 odd numbers is the same as the mathematical problem 1+3+5+7+9+11+...+99, rewrite the following sentence as a mathematical problem: the sum of the first 150 odd numbers is the same as ......
13. Given that the sum of the first 50 odd numbers is the same as the mathematical problem 1+3+5+7+9+11+...+99, rewrite the following sentence as a mathematical problem: the sum of the first 242 odd numbers is the same as ......
14. Given that the sum of the first 50 odd numbers is the same as the mathematical problem 1+3+5+7+9+11+...+99, rewrite the following sentence as a mathematical problem: the sum of the first 400 odd numbers is the same as ......
15. 55+57+59+...+311=?
16. 213+215+217+...+501=?
17. 457+459+461+...+975=?
18. 99+101+103+...+445=?
19. 25+27+29+...+1013=?
20. 77+79+81...+367=?