30

Thirty is the natural number that follows twenty-nine and precedes thirty-one. In the decimal system it is written as 30; in Roman numerals it is XXX. In binary it is 11110; in hexadecimal it is 1E; in octal it is 36.

Mathematically, 30 is an even composite number with prime factorization 2 × 3 × 5. Its divisors are 1, 2, 3, 5, 6, 10, 15, and 30. The sum of its proper divisors is 42, so 30 is an abundant number. It is pronic, equal to 5 × 6, and it is a Harshad number because it is divisible by the sum of its digits (3 + 0 = 3).

In science, 30 is the atomic number of zinc (Zn). In geometry and time, 30 degrees is a common angle; 30 minutes comprise half an hour. In computing, decimal 30 corresponds to the ASCII control character Record Separator (0x1E).

Culturally, Judas Iscariot’s thirty pieces of silver are a notable biblical reference. The 30th anniversary is traditionally associated with the pearl. The familiar rhyme Thirty days hath September, April, June, and November lists the months with 30 days.