ILL 1984 Problem 16

The harmonic table is a triangular array:

$1$

$\frac 12 \frac 12$

$\frac 13 \frac 16 \frac 13$

$\frac 14 \frac 1{12} \frac 1{12} \frac 14$

Where $a_{n,1} = \frac 1n$ and $a_{n,k+1} = a_{n-1,k} - a_{n,k}$ for $1 \leq k \leq n-1.$ Find the harmonic mean of the $1985^{th}$ row.