21613525 has 6 divisors (see below), whose sum is σ = 26800802. Its totient is φ = 17290800.

The previous prime is 21613517. The next prime is 21613577. The reversal of 21613525 is 52531612.

It can be written as a sum of positive squares in 3 ways, for example, as 324 + 21613201 = 18^2 + 4649^2 .

It is not a de Polignac number, because 21613525 - 2³ = 21613517 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: 864541 = 21613525 / (2 + 1 + 6 + 1 + 3 + 5 + 2 + 5).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21613525.

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, 432246 + ... + 432295.

Almost surely, 2^21613525 is an apocalyptic number.

21613525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21613525 is a deficient number, since it is larger than the sum of its proper divisors (5187277).

21613525 is an equidigital number, since it uses as much as digits as its factorization.

21613525 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 864551 (or 864546 counting only the distinct ones).

The product of its digits is 1800, while the sum is 25.

The square root of 21613525 is about 4649.0348460729. The cubic root of 21613525 is about 278.5534451933.

The spelling of 21613525 in words is "twenty-one million, six hundred thirteen thousand, five hundred twenty-five".