21505525 has 12 divisors (see below), whose sum is σ = 27318564. Its totient is φ = 16784000.

The previous prime is 21505513. The next prime is 21505531. The reversal of 21505525 is 52550512.

It is a happy number.

It can be written as a sum of positive squares in 6 ways, for example, as 3587236 + 17918289 = 1894^2 + 4233^2 .

It is not a de Polignac number, because 21505525 - 2⁹ = 21505013 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (25).

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 21505525.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9466 + ... + 11515.

It is an arithmetic number, because the mean of its divisors is an integer number (2276547).

Almost surely, 2^21505525 is an apocalyptic number.

21505525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21505525 is a deficient number, since it is larger than the sum of its proper divisors (5813039).

21505525 is a wasteful number, since it uses less digits than its factorization.

21505525 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21032 (or 21027 counting only the distinct ones).

The product of its (nonzero) digits is 2500, while the sum is 25.

The square root of 21505525 is about 4637.4049855496. The cubic root of 21505525 is about 278.0887050226.

The spelling of 21505525 in words is "twenty-one million, five hundred five thousand, five hundred twenty-five".