21661525 has 6 divisors (see below), whose sum is σ = 26860322. Its totient is φ = 17329200.

The previous prime is 21661517. The next prime is 21661531. The reversal of 21661525 is 52516612.

It can be written as a sum of positive squares in 3 ways, for example, as 1653796 + 20007729 = 1286^2 + 4473^2 .

It is not a de Polignac number, because 21661525 - 2³ = 21661517 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21661493 and 21661502.

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, 433206 + ... + 433255.

Almost surely, 2^21661525 is an apocalyptic number.

21661525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21661525 is a deficient number, since it is larger than the sum of its proper divisors (5198797).

21661525 is an equidigital number, since it uses as much as digits as its factorization.

21661525 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 866471 (or 866466 counting only the distinct ones).

The product of its digits is 3600, while the sum is 28.

The square root of 21661525 is about 4654.1943448893. The cubic root of 21661525 is about 278.7594994986.

The spelling of 21661525 in words is "twenty-one million, six hundred sixty-one thousand, five hundred twenty-five".