A vector is a fixed-length array with constant-time access and update of the vector slots, which are numbered from 0 to one less than the number of slots in the vector. Two vectors are equal? if they have the same length, and if the values in corresponding slots of the vectors are equal?. A vector can be mutable or immutable. When an immutable vector is provided to a procedure like vector-set!, the exn:fail:contract exception is raised. Vectors generated by the default reader (see Reading Strings) are immutable. A vector can be used as a single-valued sequence (see Sequences). The elements of the vector serve as elements of the sequence. See also in-vector. A literal or printed vector starts with #(, optionally with a number between the # and (. See Reading Vectors for information on reading vectors and Printing Vectors for information on printing vectors. Source.