random

(random n)

Returns a pseudo-random number from 0 up to but not including n: an exact integer when n is an exact positive integer, an inexact number when n is inexact. n must be positive; (random 0) is an error. A Structure and Interpretation of Computer Programs (SICP)/MIT name, not R7RS: no library exports it, so it is visible only to a file with no import and at the REPL.