FUNCTION f(n)
   IF n<2 THEN
      LET f=13
   ELSE
      LET f=(14-n)*f(n-1)
   END IF
END FUNCTION

PRINT 
PRINT 13;": ";f(13)
PRINT
PRINT " 13! =";1*2*3*4*5*6*7*8*9*10*11*12*13
PRINT
END