set.seed(12345)

n<-10000;
df1_list<-c(5,9,15,38)
df2_list<-c(10,10,20,40)
par(mfrow=c(2,2))

for (i in 1:length(df1_list)) {
  hist(rf(n, df1=df1_list[i], df2=df2_list[i], ncp=0), breaks=100, xlab="f", main=paste("df1=", df1_list[i], "df2=", df2_list[i]))
}