21645725 has 6 divisors (see below), whose sum is σ = 26840730. Its totient is φ = 17316560.

The previous prime is 21645707. The next prime is 21645733. The reversal of 21645725 is 52754612.

It can be written as a sum of positive squares in 3 ways, for example, as 13924 + 21631801 = 118^2 + 4651^2 .

It is not a de Polignac number, because 21645725 - 2¹⁶ = 21580189 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21645691 and 21645700.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 432890 + ... + 432939.

It is an arithmetic number, because the mean of its divisors is an integer number (4473455).

Almost surely, 2^21645725 is an apocalyptic number.

21645725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21645725 is a deficient number, since it is larger than the sum of its proper divisors (5195005).

21645725 is an equidigital number, since it uses as much as digits as its factorization.

21645725 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 865839 (or 865834 counting only the distinct ones).

The product of its digits is 16800, while the sum is 32.

The square root of 21645725 is about 4652.4966415893. The cubic root of 21645725 is about 278.6917069280.

The spelling of 21645725 in words is "twenty-one million, six hundred forty-five thousand, seven hundred twenty-five".