21238821 has 24 divisors (see below), whose sum is σ = 32914560. Its totient is φ = 13534488.

The previous prime is 21238757. The next prime is 21238843. The reversal of 21238821 is 12883212.

It is not a de Polignac number, because 21238821 - 2⁶ = 21238757 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21238891) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 13540 + ... + 15026.

It is an arithmetic number, because the mean of its divisors is an integer number (1371440).

Almost surely, 2^21238821 is an apocalyptic number.

It is an amenable number.

21238821 is a deficient number, since it is larger than the sum of its proper divisors (11675739).

21238821 is a wasteful number, since it uses less digits than its factorization.

21238821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1542 (or 1513 counting only the distinct ones).

The product of its digits is 1536, while the sum is 27.

The square root of 21238821 is about 4608.5595363410. The cubic root of 21238821 is about 276.9343334634.

The spelling of 21238821 in words is "twenty-one million, two hundred thirty-eight thousand, eight hundred twenty-one".