**Problem : **
Find an explicit formula for the following sequence:
1, 3, 5, 7, 9,....

**Problem : **
Find three explicit formulas for the following sequence:
-1, 1, -1, 1, -1, 1,…
(Hint: Use trigonometric functions, too).

**Problem : **
What is the
11
th term of the sequence
*a*
_{n} = 2*n* - 6
?

**Problem : **
Calculate
(4*i* - 5)
.

**Problem : **
Calculate
5(*k* + 2)
.

**Problem : **
Let
*a*
_{n} = 4*n*
^{2}
. What is the sum of the first five terms of
*a*
?