21807421 has 4 divisors (see below), whose sum is σ = 22955200. Its totient is φ = 20659644.

The previous prime is 21807419. The next prime is 21807431. The reversal of 21807421 is 12470812.

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 21807421 - 2¹ = 21807419 is a prime.

It is a super-2 number, since 2×21807421² = 951127221342482, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21807431) 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, 573861 + ... + 573898.

It is an arithmetic number, because the mean of its divisors is an integer number (5738800).

Almost surely, 2^21807421 is an apocalyptic number.

It is an amenable number.

21807421 is a deficient number, since it is larger than the sum of its proper divisors (1147779).

21807421 is a wasteful number, since it uses less digits than its factorization.

21807421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1147778.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21807421 is about 4669.8416461375. The cubic root of 21807421 is about 279.3839388926.

The spelling of 21807421 in words is "twenty-one million, eight hundred seven thousand, four hundred twenty-one".