21364821 has 6 divisors (see below), whose sum is σ = 30860310. Its totient is φ = 14243208.

The previous prime is 21364817. The next prime is 21364841. The reversal of 21364821 is 12846312.

21364821 is a `hidden beast` number, since 2 + 13 + 648 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 13242321 + 8122500 = 3639^2 + 2850^2 .

It is not a de Polignac number, because 21364821 - 2² = 21364817 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21364841) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1186926 + ... + 1186943.

It is an arithmetic number, because the mean of its divisors is an integer number (5143385).

Almost surely, 2^21364821 is an apocalyptic number.

It is an amenable number.

21364821 is a deficient number, since it is larger than the sum of its proper divisors (9495489).

21364821 is a wasteful number, since it uses less digits than its factorization.

21364821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2373875 (or 2373872 counting only the distinct ones).

The product of its digits is 2304, while the sum is 27.

The square root of 21364821 is about 4622.2095365745. The cubic root of 21364821 is about 277.4808947158.

The spelling of 21364821 in words is "twenty-one million, three hundred sixty-four thousand, eight hundred twenty-one".