HOW TO RETURN hailstone n:
    PUT {} IN seq
    WHILE 1=1:
        PUT n IN seq[#seq]
        SELECT:
            n=1: RETURN seq
            n mod 2=0: PUT floor(n/2) IN n
            n mod 2=1: PUT 3*n+1 IN n
    RETURN seq

PUT hailstone 27 IN h27
WRITE "Length of Hailstone sequence for 27:", #h27/
WRITE "First 4 elements:", h27[0], h27[1], h27[2], h27[3]/
WRITE "Last 4 elements:", h27[#h27-4], h27[#h27-3], h27[#h27-2], h27[#h27-1]/

PUT 0, 0 IN longest, length
FOR n IN {1..100000}:
    PUT hailstone n IN hn
    IF #hn > length:
        PUT n, #hn IN longest, length

WRITE longest, "has the longest hailstone sequence < 100,000, of length:", length/