to hail.next :n
  output ifelse equal? 0 modulo :n 2 [:n/2] [3*:n + 1]
end

to hail.seq :n
  if :n = 1 [output [1]]
  output fput :n hail.seq hail.next :n
end

show hail.seq 27
show count hail.seq 27

to max.hail :n
  localmake "max.n 0
  localmake "max.length 0
  repeat :n [if greater? count hail.seq repcount  :max.length [
    make "max.n repcount
    make "max.length count hail.seq repcount
  ] ]
  (print :max.n [has hailstone sequence length] :max.length)
end

max.hail 100000