21036421 has 16 divisors (see below), whose sum is σ = 25254144. Its totient is φ = 17132544.

The previous prime is 21036413. The next prime is 21036443. The reversal of 21036421 is 12463012.

It is a cyclic number.

It is not a de Polignac number, because 21036421 - 2³ = 21036413 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21036451) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 30735 + ... + 31411.

It is an arithmetic number, because the mean of its divisors is an integer number (1578384).

Almost surely, 2^21036421 is an apocalyptic number.

It is an amenable number.

21036421 is a deficient number, since it is larger than the sum of its proper divisors (4217723).

21036421 is a wasteful number, since it uses less digits than its factorization.

21036421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 900.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21036421 is about 4586.5478303404. The cubic root of 21036421 is about 276.0518219923.

Adding to 21036421 its reverse (12463012), we get a palindrome (33499433).

The spelling of 21036421 in words is "twenty-one million, thirty-six thousand, four hundred twenty-one".