Although the number of days in a month vary, 30 is used to estimate.. 30 is the first sphenic number, that is the smallest number with 3 distinct prime divisors 30 is the largest number with the property that all smaller numbers relatively prime to it are prime.
But, almost two years after much of it was completed, adele did release 30.. The number of days in the months april, june, september and november (and in unusual circumstances february—see february 30).