C# Set SpriteRenderer Sprite and "sub-sprite"

If I have a Sprite which I have sliced so that it has 256 different sprites in it and I want to set the SpriteRenderer to use for example "sprites_42", how would I do that?

 

If its not meant for runtime, just drag the sprite from the project view into SpriteRenderer field.

For runtime you could create a public sprite[] allSprites; and do a SpriteRenderer.sprite = allSprites[someIndex];

 

It's meant for runtime. The thing is that the Sprite object holds all the sprites but I do not know how to access different ones through the script, all I get when loading the Sprite using Resources.Load is the first Sprite, which would be "sprites_0".