  Interaction of two skyrmions stabilized by the ferromagnetic exchange,
Dzyaloshinskii-Moriya interaction (DMI), and external magnetic field has been
studied numerically on a 2D lattice of size large compared to the separation,
$d$, between the skyrmions. We show that two skyrmions of the same chirality
(determined by the symmetry of the crystal) repel. In accordance with earlier
analytical results, their long-range pair interaction falls out with the
separation as $\exp(-d/\delta_H)$, where $\delta_H$ is the magnetic screening
length, independent of the DMI. The prefactor in this expression depends on the
DMI that drives the repulsion. The latter results in the spiral motion of the
two skyrmions around each other, with the separation between them growing
logarithmically with time. When two skyrmions of the total topological charge
$Q = 2$ are pushed close to each other, the discreteness of the atomic lattice
makes them collapse into one skyrmion of charge $Q = 1$ below a critical
separation. Experiment is proposed that would allow one to measure the
interaction between two skyrmions by holding them in positions with two
magnetic tips. Our findings should be of value for designing topologically
protected magnetic memory based upon skyrmions.
