21309524 has 12 divisors (see below), whose sum is σ = 38494848. Its totient is φ = 10311000.

The previous prime is 21309511. The next prime is 21309527. The reversal of 21309524 is 42590312.

It is a junction number, because it is equal to n+sod(n) for n = 21309493 and 21309502.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309527) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 85802 + ... + 86049.

It is an arithmetic number, because the mean of its divisors is an integer number (3207904).

Almost surely, 2^21309524 is an apocalyptic number.

It is an amenable number.

21309524 is a deficient number, since it is larger than the sum of its proper divisors (17185324).

21309524 is a wasteful number, since it uses less digits than its factorization.

21309524 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171886 (or 171884 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 21309524 is about 4616.2239980313. The cubic root of 21309524 is about 277.2412933965.

Adding to 21309524 its reverse (42590312), we get a palindrome (63899836).

The spelling of 21309524 in words is "twenty-one million, three hundred nine thousand, five hundred twenty-four".