21552421 has 4 divisors (see below), whose sum is σ = 23511744. Its totient is φ = 19593100.

The previous prime is 21552383. The next prime is 21552437. The reversal of 21552421 is 12425512.

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 a de Polignac number, because none of the positive numbers 2^k-21552421 is a prime.

It is a super-2 number, since 2×21552421² = 929013701922482, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21552392 and 21552401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21552451) 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, 979645 + ... + 979666.

It is an arithmetic number, because the mean of its divisors is an integer number (5877936).

Almost surely, 2^21552421 is an apocalyptic number.

It is an amenable number.

21552421 is a deficient number, since it is larger than the sum of its proper divisors (1959323).

21552421 is a wasteful number, since it uses less digits than its factorization.

21552421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1959322.

The product of its digits is 800, while the sum is 22.

The square root of 21552421 is about 4642.4585081614. The cubic root of 21552421 is about 278.2906962151.

Adding to 21552421 its reverse (12425512), we get a palindrome (33977933).

The spelling of 21552421 in words is "twenty-one million, five hundred fifty-two thousand, four hundred twenty-one".