21809725 has 24 divisors (see below), whose sum is σ = 32730048. Its totient is φ = 14073600.

The previous prime is 21809719. The next prime is 21809737. The reversal of 21809725 is 52790812.

It is not a de Polignac number, because 21809725 - 2⁵ = 21809693 is a prime.

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

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 (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 691 + ... + 6640.

It is an arithmetic number, because the mean of its divisors is an integer number (1363752).

Almost surely, 2^21809725 is an apocalyptic number.

21809725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21809725 is a deficient number, since it is larger than the sum of its proper divisors (10920323).

21809725 is a wasteful number, since it uses less digits than its factorization.

21809725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7365 (or 7360 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 21809725 is about 4670.0883289291. The cubic root of 21809725 is about 279.3937777134.

The spelling of 21809725 in words is "twenty-one million, eight hundred nine thousand, seven hundred twenty-five".