Mammillaria nivosa (20 seeds)

It is a  relatively rapidly growing and easily flowering species that will make large clumps given the best conditions. Most plants will offset readily, and clumps can be produced in a few years.
Water regularly in summer, but do not overwater (Rot prone) Use pot with good drainage and a very porous potting media,  keep dry in winter. Feed with a high potassium fertilizer  in summer. Avoid any frost. Reputedly sensitive to low temperatures, but less so if kept on the dry side prior to, and during, cold weather. Outside full sun or afternoon shade, inside it needs bright light, and some direct sun. Tends to bronze in strong light, which encourages flowering and heavy wool and spine production.
Be careful when you repot Mammillaria nivosa. Its spine is very sharp and hard. You should use gloves or wrap the cactus with thick newspaper. They may make it easier.

All seeds are fresh of this season and obtained from my personal collection.
NOTE: cactus seeds could be sown in any season under control environment, however if you wanna go with nature then best time to sow the seeds is early spring/summer )

(check my collection at https://www.instagram.com/planetcactus