The story
The contraharmonic mean of two variables is at the same distance from their arithmetic mean as their harmonic mean but on the opposite side.
Etymology from Wiktionary, CC BY-SA 4.0.
contraharmonic mean
Today it means: A type of average calculated as the arithmetic mean of the squares of the values divided by the arithmetic mean of the values, i.e. C=(x_1²+x_2²+...+x_n²)/n/(x_1+x_2+...+x_n)/norC(x_1,x_2,...,x_n)=x_1²+x_2²+...+x_n²/x_1+x_2+...+x_n Full definition →