z <- function(x) floor(x); R <- function(x) runif(x)
i <- 1; while(i==1){x<- z(R(2)*13+2);x[1]<- x[1]*2^z(R(1)*6-3);if( x[1]/x[2]!=z(x[1]/x[2])) i<- 0}
F <- MASS::fractions(x[1]/x[2]); print(x[1]/x[2],16)