Which is a possible expression for the series
–6 –12 –24 –48 –96 –192

We notice that ; -6, -12, -24, -48 , 96, -19 is a geometric progression with r = -2
which is : -3(2), -3(4), -3(8), -3(16). -3(32), -3(32)
OR          -3(2), -3(2²) -3(2³), -3(2⁴), -3(2⁵), -3(2⁶)

 That is:
 ₆
Σ  (-3)(2)^k
k=₁