Based on the pattern in the table, what is the value of a?

Powers of 2
Value
2 Superscript negative 1
One-half
2 Superscript negative 2
One-fourth
2 Superscript negative 3
one-eighth
2 Superscript negative 4
StartFraction 1 Over 16 EndFraction
2 Superscript negative 5
StartFraction 1 Over 32 EndFraction
2 Superscript negative 6
a

Negative 64
Negative 12
StartFraction 1 Over 16 EndFraction
StartFraction 1 Over 64 EndFraction