At what point (in Ohms) can I skip a resistor?

I'm assuming 20 LED's in parallel? With a forward V/D of 3.7v, at 20mA. R=(Vs-Vf) / I max. R= 65 ohms @1/4 watt LED's are current dependent devices, and must have a current limiting resistor. Just an increase of a few micro-volts can drive the current to the point where the magic smoke comes out.