Need more information. Are they high power LEDs or standard 5mm type? What is the forward voltage of the LEDs. What is the voltage that will be supplied?If they are high power LEDs you want to run them in series and constant current regulate them. Otherwise, you can have an issue where one LED starts conducting more than another and end up in thermal run away (where the LED conducting more causes it to get hotter, which lowers its resistance, which causes it to conduct more until finally it is taking more current than it can handle and it burns out).If they are the other type. Then a convenient website is the Series parallel array calculator http://led.linear1.org/led.wizYou input the supplied voltage, the forward voltage of the LEDs, the current you want to run the LEDs at and the number of LEDs. It does the rest outputing an array with the required resistors and their sizes.