21155825 has 6 divisors (see below), whose sum is σ = 26233254. Its totient is φ = 16924640.

The previous prime is 21155789. The next prime is 21155839. The reversal of 21155825 is 52855112.

It can be written as a sum of positive squares in 3 ways, for example, as 2085136 + 19070689 = 1444^2 + 4367^2 .

It is not a de Polignac number, because 21155825 - 2²² = 16961521 is a prime.

It is a Duffinian 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, 423092 + ... + 423141.

It is an arithmetic number, because the mean of its divisors is an integer number (4372209).

Almost surely, 2^21155825 is an apocalyptic number.

21155825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21155825 is a deficient number, since it is larger than the sum of its proper divisors (5077429).

21155825 is an equidigital number, since it uses as much as digits as its factorization.

21155825 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 846243 (or 846238 counting only the distinct ones).

The product of its digits is 4000, while the sum is 29.

The square root of 21155825 is about 4599.5461732654. The cubic root of 21155825 is about 276.5731325245.

The spelling of 21155825 in words is "twenty-one million, one hundred fifty-five thousand, eight hundred twenty-five".