21210421 has 4 divisors (see below), whose sum is σ = 21239712. Its totient is φ = 21181132.

The previous prime is 21210389. The next prime is 21210433. The reversal of 21210421 is 12401212.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21210421 - 2⁵ = 21210389 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 (21210461) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13531 + ... + 15016.

It is an arithmetic number, because the mean of its divisors is an integer number (5309928).

Almost surely, 2^21210421 is an apocalyptic number.

It is an amenable number.

21210421 is a deficient number, since it is larger than the sum of its proper divisors (29291).

21210421 is an equidigital number, since it uses as much as digits as its factorization.

21210421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29290.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21210421 is about 4605.4772825409. The cubic root of 21210421 is about 276.8108419370.

Adding to 21210421 its reverse (12401212), we get a palindrome (33611633).

The spelling of 21210421 in words is "twenty-one million, two hundred ten thousand, four hundred twenty-one".