**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 11th 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*?

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