How to set the number of objects created for Sequence (Laravel 8)

I’m trying to create 30 news using Seeder and Factory. But I need to create 10 news with a non-empty field value published_at (Carbon) а для остальных случайное значение (Carbon/NULL)

In the documentation I saw such an example, it creates 5 records with the value admin (Y) and 5 more records with the value admin (N)

User::factory()
    ->count(10)
    ->state(new Sequence(
        ['admin' => 'Y'],
        ['admin' => 'N'],
        ))
        ->create();

So far I’m using this code, but I can’t figure out how to add the number of records being created with a certain parameter value published_at. For example, 10 with Carbon and 20 with NULL.

/** ArticleSeeder */
Article::factory()
    ->count(30)
    ->state(new Sequence([
        'published_at' => Factory::create()->dateTimeBetween(
            now()->startOfMonth(),
            now()->endOfMonth()
        ),
    ]))
    ->create();