21456569 has 4 divisors (see below), whose sum is σ = 21468660. Its totient is φ = 21444480.

The previous prime is 21456563. The next prime is 21456577. The reversal of 21456569 is 96565412.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 8761600 + 12694969 = 2960^2 + 3563^2 .

It is a cyclic number.

It is not a de Polignac number, because 21456569 - 2⁸ = 21456313 is a prime.

It is a super-2 number, since 2×21456569² = 920768706503522, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21456563) 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, 2804 + ... + 7125.

It is an arithmetic number, because the mean of its divisors is an integer number (5367165).

Almost surely, 2^21456569 is an apocalyptic number.

It is an amenable number.

21456569 is a deficient number, since it is larger than the sum of its proper divisors (12091).

21456569 is an equidigital number, since it uses as much as digits as its factorization.

21456569 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12090.

The product of its digits is 64800, while the sum is 38.

The square root of 21456569 is about 4632.1235950695. The cubic root of 21456569 is about 277.8775274409.

The spelling of 21456569 in words is "twenty-one million, four hundred fifty-six thousand, five hundred sixty-nine".