21455421 has 8 divisors (see below), whose sum is σ = 30807840. Its totient is φ = 13203312.

The previous prime is 21455393. The next prime is 21455429. The reversal of 21455421 is 12455412.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21455421 - 2⁷ = 21455293 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21455391 and 21455400.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21455429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 275031 + ... + 275108.

It is an arithmetic number, because the mean of its divisors is an integer number (3850980).

Almost surely, 2^21455421 is an apocalyptic number.

It is an amenable number.

21455421 is a deficient number, since it is larger than the sum of its proper divisors (9352419).

21455421 is a wasteful number, since it uses less digits than its factorization.

21455421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 550155.

The product of its digits is 1600, while the sum is 24.

The square root of 21455421 is about 4631.9996761658. Note that the first 3 decimals coincide. The cubic root of 21455421 is about 277.8725715524.

Subtracting from 21455421 its reverse (12455412), we obtain a palindrome (9000009).

The spelling of 21455421 in words is "twenty-one million, four hundred fifty-five thousand, four hundred twenty-one".