‘Ek number’ is more of a Maharashtra thing IMO. You’ll hear it quite frequently in MH state
Ek number was commonly used in my childhood days in Mumbai and it means "First class" or "Classic". Typical uses: ek number joke, ek number daaru (daaru = alcohol, liquor), ek number maal (First class, good looking, hot girl), ek number vada pav (classic food dish) etc.