KöMaL 2021 K709

A family are planning to grow a special type of onion in their garden. They want to eat 400 onion bulbs each year. The onion is grown from a seed. Each onion plant can produce 51 seeds every year if we let it. However, once an onion plant has gone into seeds, its bulb will dissolve during growing the seeds. What is the minimum number of seeds the family need to buy in order to launch the onion project so that they can have the desired quantity of onion bulbs to eat, and they never need to buy seeds any more?