**broken link removed** is a reasonable calculator for working out the values and arrangements.
It's shortcomings are that it will design around too many LEDs for the supply voltage, leaving a very small voltage drop across the limiting resistors.
Also, if more than one string of LEDs are needed, it doesn't even them up. For instance on 32 V, with 3 V LEDs, and you want 16 of them, it will put 10 in one string and 6 in another. In the string of 10 LEDs, there is 2 V across the resistor. That is a very small proportion of the 32V, and if the supply drops to 31 V, the LED current halves.
You would be better to use two strings of 8 LEDs, leaving 8 V across the resistor.