21566401 has 4 divisors (see below), whose sum is σ = 22310100. Its totient is φ = 20822704.

The previous prime is 21566393. The next prime is 21566407. The reversal of 21566401 is 10466512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 18147600 + 3418801 = 4260^2 + 1849^2 .

It is a cyclic number.

It is not a de Polignac number, because 21566401 - 2³ = 21566393 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21566407) 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, 371806 + ... + 371863.

It is an arithmetic number, because the mean of its divisors is an integer number (5577525).

Almost surely, 2^21566401 is an apocalyptic number.

It is an amenable number.

21566401 is a deficient number, since it is larger than the sum of its proper divisors (743699).

21566401 is an equidigital number, since it uses as much as digits as its factorization.

21566401 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 743698.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21566401 is about 4643.9639318151. The cubic root of 21566401 is about 278.3508543916.

The spelling of 21566401 in words is "twenty-one million, five hundred sixty-six thousand, four hundred one".