a semiperfect number
a harshad number
a square pyramidal number
Zinc’s atomic number is 30
between 29 and 31
the number of variations in Bach’s Goldberg Variations
the second point won in a tennis match
according to Albert Camus in ‘”The Myth of Sisyphus” the age of thirty is a crucial period in the life of a man, for at that age he gains a new awareness of the meaning of time.