I've encountered a lot (!) of unlucky prime numbers that I'm trying to FFT in too many places, and it basically stops the code. 211151 was impossibly bad, 5827 is pretty bad too. I solved the first by splitting into by-scan delining, which is better anyway. But the second is a map, in which I KNOW zero padding is OK. So... are there any functions that find the nearest reasonably efficient map size?