21561725 has 12 divisors (see below), whose sum is σ = 27242676. Its totient is φ = 16922880.

The previous prime is 21561697. The next prime is 21561733. The reversal of 21561725 is 52716512.

It can be written as a sum of positive squares in 6 ways, for example, as 1545049 + 20016676 = 1243^2 + 4474^2 .

It is not a de Polignac number, because 21561725 - 2⁸ = 21561469 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6812 + ... + 9461.

It is an arithmetic number, because the mean of its divisors is an integer number (2270223).

Almost surely, 2^21561725 is an apocalyptic number.

21561725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21561725 is a deficient number, since it is larger than the sum of its proper divisors (5680951).

21561725 is a wasteful number, since it uses less digits than its factorization.

21561725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16336 (or 16331 counting only the distinct ones).

The product of its digits is 4200, while the sum is 29.

The square root of 21561725 is about 4643.4604553070. The cubic root of 21561725 is about 278.3307357099.

The spelling of 21561725 in words is "twenty-one million, five hundred sixty-one thousand, seven hundred twenty-five".