Question
Write the first five terms of the sequence and obtain the corresponding series a1 = a2 = 2, an = an-1 - 1, n > 2.

Answer

Given: a1 = a2 = 2, an = an-1 - 1, n > 2
Putting n = 3, 4 and 5, we get
a3 = a3-1 - 1 = a2 - 1 = 2 - 1 = 1
a4 = a4-1 - 1 = a3 - 1 = 1 - 1 = 0 
a5 = a5-1 - 1 = a4 - 1 = 0 - 1 = -1
Hence the first five terms are 2, 2, 1, 0, -1.
Therefore, corresponding series is 2 + 2 + 1 + 0 + (-1) + .......

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