Alfred Stieglitz exhibited Georgia O'Keeffe's work at his New York gallery 291.
The gallery's name came from its address at 291 Fifth Avenue in Manhattan. It was founded by Stieglitz and originally known as the Little Galleries of the Photo-Secession before becoming widely identified by its address.
A friend showed Stieglitz some of O'Keeffe's abstract charcoal drawings in 1915. He exhibited them at 291 in 1916 without initially telling O'Keeffe, and the display helped bring her work to the attention of New York's modern-art community.
Stieglitz later operated other galleries, including the Intimate Gallery and An American Place. Those names are therefore plausible mix-ups, but 291 was the gallery associated with O'Keeffe's first New York exhibition.