A Prime Clock Divider accepts a CV input as a gate, and creates a number of
beats based on input triggers.  Each time a beat occurs (when a CV value
goes from under 1.7 to 1.7 or above), a value of 1.7 is output for one
half of that beat.
The outputs are based on the division of each row, from 1 to 19, but only
including the prime numbers.  If the current count is equal to any of those,
then that output is high, otherwise the output is low.
     1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16 17 18 19
/2      x
/3         x
/5                x
/7                     x
/11                                 x
/13                                       x
/17                                                   x
/19                                                         x