subr first
   n = 1 ; d = 1
.
proc next . .
   n = 2 * (n div d) * d + d - n
   swap n d
.
print "The first 20 terms of the Calkwin-Wilf sequence are:"
first
for i to 20
   write n & "/" & d & " "
   next
.
print ""
# 
first
i = 1
while n <> 83116 or d <> 51639
   next
   i += 1
.
print "83116/51639 is at position " & i
