21930 has 32 divisors (see below), whose sum is σ = 57024. Its totient is φ = 5376.

The previous prime is 21929. The next prime is 21937. The reversal of 21930 is 3912.

21930 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (15).

21930 is an undulating number in base 13.

21930 is strictly pandigital in base 6.

It is a plaindrome in base 4 and base 16.

It is a zygodrome in base 4 and base 16.

It is not an unprimeable number, because it can be changed into a prime (21937) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 489 + ... + 531.

It is an arithmetic number, because the mean of its divisors is an integer number (1782).

2²¹⁹³⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21930, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28512).

21930 is an abundant number, since it is smaller than the sum of its proper divisors (35094).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21930 is a wasteful number, since it uses less digits than its factorization.

21930 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70.

The product of its (nonzero) digits is 54, while the sum is 15.

The square root of 21930 is about 148.0878117875. The cubic root of 21930 is about 27.9906431320.

Adding to 21930 its sum of digits (15), we get a triangular number (21945 = T₂₀₉).

The spelling of 21930 in words is "twenty-one thousand, nine hundred thirty".