1221 Avenue of the Americas
…by the Rockefeller family's architect, Wallace Harrison, of the architectural firm Harrison & Abramovitz. Their letters correspond to their height. 1251 Avenue of the Americas is the "X" Building as it is the tallest at 750 ft (229 m) and 54 stories, and was the first completed, in 1971. The "Y" is 1221 Avenue of the Americas…