OPENW 1
CLEARW 1
'
DIM f%(20001) ! sum of proper factors for each n
FOR i%=1 TO 20000
  f%(i%)=@sum_proper_divisors(i%)
NEXT i%
' look for pairs
FOR i%=1 TO 20000
  FOR j%=i%+1 TO 20000
    IF f%(i%)=j% AND i%=f%(j%)
      PRINT "Amicable pair ";i%;" ";j%
    ENDIF
  NEXT j%
NEXT i%
'
PRINT
PRINT "-- found all amicable pairs"
~INP(2)
CLOSEW 1
'
' Compute the sum of proper divisors of given number
'
FUNCTION sum_proper_divisors(n%)
  LOCAL i%,sum%,root%
  '
  IF n%>1 ! n% must be 2 or larger
    sum%=1 ! start with 1
    root%=SQR(n%) ! note that root% is an integer
    ' check possible factors, up to sqrt
    FOR i%=2 TO root%
      IF n% MOD i%=0
        sum%=sum%+i% ! i% is a factor
        IF i%*i%<>n% ! check i% is not actual square root of n%
          sum%=sum%+n%/i% ! so n%/i% will also be a factor
        ENDIF
      ENDIF
    NEXT i%
  ENDIF
  RETURN sum%
ENDFUNC