Hi, welcome to g o y, depends on the size of the plants you have bought, if they're quite small, then I would suggest 3 or 4, to give a massed effect, Derek.

It would also depend on what species of cyclamen you have bought, some tubers grow very large. I would start with three or five tubers, odd number, and be prepared to remove some in a few years time. I have known Cyclamen hederifolium tubers that will easily fill an 8" pot!