21630 has 32 divisors (see below), whose sum is σ = 59904. Its totient is φ = 4896.

The previous prime is 21617. The next prime is 21647. The reversal of 21630 is 3612.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is a nialpdrome in base 15.

It is a congruent number.

It is an unprimeable number.

21630 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 159 + ... + 261.

It is an arithmetic number, because the mean of its divisors is an integer number (1872).

2²¹⁶³⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21630, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29952).

21630 is an abundant number, since it is smaller than the sum of its proper divisors (38274).

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

21630 is a wasteful number, since it uses less digits than its factorization.

21630 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 120.

The product of its (nonzero) digits is 36, while the sum is 12.

The square root of 21630 is about 147.0714112260. The cubic root of 21630 is about 27.8624203395.

Multiplying 21630 by its sum of digits (12), we get a triangular number (259560 = T₇₂₀).

The spelling of 21630 in words is "twenty-one thousand, six hundred thirty".