21645425 has 6 divisors (see below), whose sum is σ = 26840358. Its totient is φ = 17316320.

The previous prime is 21645419. The next prime is 21645439. The reversal of 21645425 is 52454612.

It can be written as a sum of positive squares in 3 ways, for example, as 2835856 + 18809569 = 1684^2 + 4337^2 .

It is not a de Polignac number, because 21645425 - 2¹⁸ = 21383281 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

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, 432884 + ... + 432933.

It is an arithmetic number, because the mean of its divisors is an integer number (4473393).

Almost surely, 2^21645425 is an apocalyptic number.

21645425 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21645425 is a deficient number, since it is larger than the sum of its proper divisors (5194933).

21645425 is an equidigital number, since it uses as much as digits as its factorization.

21645425 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 865827 (or 865822 counting only the distinct ones).

The product of its digits is 9600, while the sum is 29.

The square root of 21645425 is about 4652.4644007236. The cubic root of 21645425 is about 278.6904194082.

The spelling of 21645425 in words is "twenty-one million, six hundred forty-five thousand, four hundred twenty-five".