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We consider the stability problem for the stationary rotation of a regular point vortex ngon lying outside a circular domain. After the article of Havelock (1931), the complete solution of the problem remains unclear in the case 2 ≤ n ≤ 6. We obtain the exhaustive results for evenly many vortices n = 2, 4, 6.

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The model of point vortices located outside a circular domain is considered. The review of stability and instability conditions of a system of identical point vortices located uniformly on a circle is given. Theoretical results are confirmed by numerical calculations.