Standard Deviation in R Seems to be Returning the Wrong Answer - Am I Doing Something Wrong?

Question

A simple example of calculating standard dev:

d <- c(2,4,4,4,5,5,7,9)
sd(d)

yields

[1] 2.13809

but

Answer 1

When I want the population variance or standard deviation (n as denominator), I define these two vectorized functions.

  pop.var <- function(x) var(x) * (length(x)-1) / length(x)

  pop.sd <- function(x) sqrt(pop.var(x))

BTW, Khan Academy has a good discussion of population and sample standard deviation here.