We have given, a1 = a2 = 2 , an = an−1 - 1 ,
a1 = 2 , a2 = 2 , a3 = a2 - 1 = 2 - 1 = 1,
a4 = a3 - 1 = 1 - 1 = 0 and a5 = a4 - 1 = 0 - 1 = - 1
Hence the first five terms of the given sequence are 2, 2, 1, 0, – 1.
The corresponding series is
2 + 2 + 1 + 0 + (– 1) + .......