i = i i5 = i·i4 = i Similarly, i9 = i13 = ... = i93 = i
i2 = -1 i6 = i2·i4 = -1 i10 = i14 = ... = i94 = -1
i3 = -i i7 = i3·i4 = -i i11 = i15 = ... = i95 = -i
i4 = 1 [8 = i4·i4 = 1 i12 = i16 = ... = i96 = i
Now, adding i + i2 + i3 + i4 = 0
which will be true for all groups of 4 terms that follow, only leaving this problem:
How much is 197 + i98 + i99?