21215725 has 6 divisors (see below), whose sum is σ = 26307530. Its totient is φ = 16972560.

The previous prime is 21215693. The next prime is 21215759. The reversal of 21215725 is 52751212.

It can be written as a sum of positive squares in 3 ways, for example, as 110889 + 21104836 = 333^2 + 4594^2 .

It is not a de Polignac number, because 21215725 - 2⁵ = 21215693 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (25), and also a Moran number because the ratio is a prime number: 848629 = 21215725 / (2 + 1 + 2 + 1 + 5 + 7 + 2 + 5).

It is a self number, because there is not a number n which added to its sum of digits gives 21215725.

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, 424290 + ... + 424339.

Almost surely, 2^21215725 is an apocalyptic number.

21215725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21215725 is a deficient number, since it is larger than the sum of its proper divisors (5091805).

21215725 is an equidigital number, since it uses as much as digits as its factorization.

21215725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 848639 (or 848634 counting only the distinct ones).

The product of its digits is 1400, while the sum is 25.

The square root of 21215725 is about 4606.0530826294. The cubic root of 21215725 is about 276.8339136516.

Adding to 21215725 its reverse (52751212), we get a palindrome (73966937).

The spelling of 21215725 in words is "twenty-one million, two hundred fifteen thousand, seven hundred twenty-five".