# function pausa() defined in a previous script

N <- 100
n <- 10000
sx <- rep(0, n)
for(ns in 1:N) {
  xi <- rnorm(n)^2
  sx <- sx + xi
  hist(sx, nc=100, col='cyan', xlab='Sum X', freq=FALSE, 
       main=sprintf("ns = %d; mean = %.1f, std = %.1f ",
                    ns, mean(sx), sd(sx)))
  pausa()
}