21534021 has 6 divisors (see below), whose sum is σ = 31104710. Its totient is φ = 14356008.

The previous prime is 21533999. The next prime is 21534031. The reversal of 21534021 is 12043512.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 245025 = 4614^2 + 495^2 .

It is not a de Polignac number, because 21534021 - 2⁷ = 21533893 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21533985 and 21534003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21534031) 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, 1196326 + ... + 1196343.

Almost surely, 2^21534021 is an apocalyptic number.

It is an amenable number.

21534021 is a deficient number, since it is larger than the sum of its proper divisors (9570689).

21534021 is a wasteful number, since it uses less digits than its factorization.

21534021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2392675 (or 2392672 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21534021 is about 4640.4763764079. The cubic root of 21534021 is about 278.2114784063.

Adding to 21534021 its reverse (12043512), we get a palindrome (33577533).

The spelling of 21534021 in words is "twenty-one million, five hundred thirty-four thousand, twenty-one".