a


b

c

Duh a dear a female dear?


2.7182818

f(x)
981cm/sec/sec


6.673 x 10 ^ -11


6.6262 x 10 ^ -34


E = m · c2

Doesn't fit the sequence - "I" was next.
So following the sequence a good cryptic equation would have been:

Sq. Root -1