How to create a sequence on sheets (1/420, 2/420… 420/420) automatically?

I need to create a sequence on the sheets (1/420, 2/420… 420/420) automatically.

I tried selecting the two sequential lines and dragging them down. I tried to use custom number formats, but I couldn’t. Can you help me? Thank you 🙂

Attempt

>Solution :

Try this out:

=ARRAYFORMULA(SEQUENCE(420)&"/420")