21023821 has 8 divisors (see below), whose sum is σ = 25875584. Its totient is φ = 16634160.

The previous prime is 21023819. The next prime is 21023831. The reversal of 21023821 is 12832012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21023821 - 2¹ = 21023819 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21023831) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 115425 + ... + 115606.

It is an arithmetic number, because the mean of its divisors is an integer number (3234448).

Almost surely, 2^21023821 is an apocalyptic number.

It is an amenable number.

21023821 is a deficient number, since it is larger than the sum of its proper divisors (4851763).

21023821 is a wasteful number, since it uses less digits than its factorization.

21023821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 231051.

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 21023821 is about 4585.1740424983. The cubic root of 21023821 is about 275.9966962077.

Adding to 21023821 its reverse (12832012), we get a palindrome (33855833).

The spelling of 21023821 in words is "twenty-one million, twenty-three thousand, eight hundred twenty-one".