21991525 has 6 divisors (see below), whose sum is σ = 27269522. Its totient is φ = 17593200.

The previous prime is 21991517. The next prime is 21991561. The reversal of 21991525 is 52519912.

It can be written as a sum of positive squares in 3 ways, for example, as 3690241 + 18301284 = 1921^2 + 4278^2 .

It is not a de Polignac number, because 21991525 - 2³ = 21991517 is a prime.

It is a Duffinian number.

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, 439806 + ... + 439855.

Almost surely, 2^21991525 is an apocalyptic number.

21991525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21991525 is a deficient number, since it is larger than the sum of its proper divisors (5277997).

21991525 is an equidigital number, since it uses as much as digits as its factorization.

21991525 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 879671 (or 879666 counting only the distinct ones).

The product of its digits is 8100, while the sum is 34.

The square root of 21991525 is about 4689.5122347639. The cubic root of 21991525 is about 280.1679477120.

The spelling of 21991525 in words is "twenty-one million, nine hundred ninety-one thousand, five hundred twenty-five".