Zero, 1964. Photo: Courtesy of the Museum Folkwang, Essen; Artwork: © The Robert Indiana Legacy Initiative/Artists Rights Society (ARS), NY
Magie der Zahl in der Kunst des 20. Jahrhunderts explored how numbers, digits, and mathematical systems became central motifs and structural elements in 20th-century art. Six of Indiana's paintings, The American Gas Works (1961–62), The Demuth American Dream No. 5 (1963), The X-5 (1963), Zero (1964), Black Diamond Golden Six (1964), and Zero (1973), and his Numbers prints (1968) were included in the show.