calculator is used to find the value of the voltage adjustment resistor
required to set the output of an LM317 to a specified level. Typically R1
is 220 ohms or 240 ohms, but it could be some other value.
Check the Data Sheet for more information regarding this. Select a value for R2 and hit the Calculate button. The LM317
output value is reported in volts.
Note: The input voltage to the LM317 must be at least 1.5v
greater than the output voltage.
Note2: You can get ridiculous values with the right combination of R1 and R2. Please note the actual capability of the device from the Data Sheet.
Also check this nice LM317 Tutorial: