How many of the sample fall in each bin.
The normal curve, in the counts' own units, so that an overlay is
drawn from these numbers rather than fitted a second time:
area / (sigma * sqrt(2 * PI)) * exp(-(((x - centre) / sigma) ** 2) / 2).
The bounds of the bins, in order, one more of them than there are counts.
A histogram with the curve its counts are held to follow.