In general - no. Ideally, budgies should be kept in pairs, even if you don't plan to breed them, or you don't have the same amount of males and female (I'll go back to that later). Two is minimum, specially if you're busy and don't spend much time at home. Single budgie will feel lonely and unless you work from home and spend majority of your time at home - get two budgies minimum. Budgerigars are flock birds and that means they're "made" to live in flocks. They tend to bond in pairs leaving the odd one out. Sometimes the bird that has no pair - is bullied or chased up by other birds. If you have 2 budgies and are considering adding new bird to the flock, think if you can afford, or have enough space for 4 budgies, instead of 3. It's actually responsible decision and you need to take into account things like a noise level, that is going to increase for sure. Budgies are noisy and the more you have the louder they are. Are you ready for that? Also - it's said that males tend to be more vocal than females, so the more males you have - the more laud it will get.
The other thing is - to keep more than two budgies - you need much bigger cage. It's recommended that a cage for 2 budgies should ideally have measurements as follows: 30x18x18 inches (77x46x46 cm). The suitable, available for example on Amazon, is THIS one. On the other hand - an ideal cage for 4-6 budgies should be around 32x18x20 inches (82x46x51 cm) and you can get a perfect one HERE.
Now - is it good to have same amount of males and females? The answer to that question is quite complex. Generally - males tend to get on with each other better than females (rings some bells, doesn't it?) So if you, for some reason, prefer male budgies - go ahead, they'll be fine together. They'll bond nicely and there shouldn't be any bigger fights between them. It doesn't work the same for females though. It's not recommended to keep only females. I've heard lots of stories that budgie owners claimed their only-females couples/flocks were doing fine, but that's not that common. Female tend to be more 'moody' and like picking fights, especially with other females.
If there is an odd number of females and males and your flock is not big, let's say - you have 4 birds and 3 of them are males and 1 is female - the males may try to fight over a female when she's in breeding condition (don't worry - they won't breed if you don't get them a breeding box). But if you have 3 females and 1 male - it's likely that females may fight over territory, food, drink, toys.. the list can be long...
