главных

главных

"Main" or "primary" (genitive plural form).

'Главных' here functions as an adjective in the plural genitive case, describing 'факторов', and means 'main'.

Одним из главных факторов успеха является упорство.

One of the main factors of success is persistence.

'Главных' in this context is an adjective in the plural accusative case, modifying 'тем', and signifies 'main' or 'major'.

Мы обсудили несколько главных тем собрания.

We discussed several main topics of the meeting.

'Главных' again is an adjective, in the plural genitive case, describing 'героев', indicating 'main' or 'principal'.

Дети выучили имена главных героев книги.

The children learned the names of the book's main characters.