21725761 has 4 divisors (see below), whose sum is σ = 22426624. Its totient is φ = 21024900.

The previous prime is 21725689. The next prime is 21725773. The reversal of 21725761 is 16752712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21725761 - 2⁷ = 21725633 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 700831 = 21725761 / (2 + 1 + 7 + 2 + 5 + 7 + 6 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21725161) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 350385 + ... + 350446.

It is an arithmetic number, because the mean of its divisors is an integer number (5606656).

Almost surely, 2^21725761 is an apocalyptic number.

It is an amenable number.

21725761 is a deficient number, since it is larger than the sum of its proper divisors (700863).

21725761 is an equidigital number, since it uses as much as digits as its factorization.

21725761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 700862.

The product of its digits is 5880, while the sum is 31.

The square root of 21725761 is about 4661.0901085476. The cubic root of 21725761 is about 279.0347759652.

The spelling of 21725761 in words is "twenty-one million, seven hundred twenty-five thousand, seven hundred sixty-one".