21539825 has 24 divisors (see below), whose sum is σ = 28405920. Its totient is φ = 16156800.

The previous prime is 21539813. The next prime is 21539831. The reversal of 21539825 is 52893512.

It is a de Polignac number, because none of the positive numbers 2^k-21539825 is a prime.

It is a super-2 number, since 2×21539825² = 927928122061250, which contains 22 as substring.

It is a Curzon 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, 64910 + ... + 65240.

It is an arithmetic number, because the mean of its divisors is an integer number (1183580).

Almost surely, 2^21539825 is an apocalyptic number.

21539825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21539825 is a deficient number, since it is larger than the sum of its proper divisors (6866095).

21539825 is a wasteful number, since it uses less digits than its factorization.

21539825 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 497 (or 492 counting only the distinct ones).

The product of its digits is 21600, while the sum is 35.

The square root of 21539825 is about 4641.1017011050. The cubic root of 21539825 is about 278.2364713291.

The spelling of 21539825 in words is "twenty-one million, five hundred thirty-nine thousand, eight hundred twenty-five".