21155725 has 6 divisors (see below), whose sum is σ = 26233130. Its totient is φ = 16924560.

The previous prime is 21155723. The next prime is 21155731. The reversal of 21155725 is 52755112.

It can be written as a sum of positive squares in 3 ways, for example, as 2128681 + 19027044 = 1459^2 + 4362^2 .

It is not a de Polignac number, because 21155725 - 2¹ = 21155723 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21155693 and 21155702.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21155723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 423090 + ... + 423139.

Almost surely, 2^21155725 is an apocalyptic number.

21155725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21155725 is a deficient number, since it is larger than the sum of its proper divisors (5077405).

21155725 is an equidigital number, since it uses as much as digits as its factorization.

21155725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 846239 (or 846234 counting only the distinct ones).

The product of its digits is 3500, while the sum is 28.

The square root of 21155725 is about 4599.5353026148. The cubic root of 21155725 is about 276.5726967524.

The spelling of 21155725 in words is "twenty-one million, one hundred fifty-five thousand, seven hundred twenty-five".