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A hot blue-white star near the southern borders of the constellation Perseus, at a distance of 349 light years from Earth. It is notable as a variable star of the Alpha2 Canum Venaticorum type, growing fainter and brighter by about a tenth of a magnitude over a period of just less than three days. 21 Persei is strong in metals, which appear to unevenly distributed over its surface, causing the oscillation in its brightness. This star is also known by the variable designation LT Persei.