Just take three regular D’s and you’ll have D3. (do I really have to say it?)
Makes sense, I used the same concept addressing by Brother's kids, I call one Denise, the other Denephew.
Vitamin D with no subscript is the sunshine derived version and far the best. It is not so much when the weather is cold and one is covered up when outdoors or in the far north where the sun is at a low angle all the time. I have read that D2 is synthetic and D3 is plant derived.