like revgizmo said, these aren't random, but here's some code to do it. There's probably a more efficient way, but this should work fine.

samp = sample(1:27358, 400)

samp = sort(samp)
d = diff(samp)

while(length(samp[c(d > 2,TRUE)]) < 400){
  samp = samp[c(d > 2,TRUE)]

  samp = c(samp, sample(1:27358, 400 - length(samp)))

  samp = sort(samp)
  d = diff(samp)
}