21531587 has 16 divisors (see below), whose sum is σ = 27078144. Its totient is φ = 16770600.

The previous prime is 21531527. The next prime is 21531599. The reversal of 21531587 is 78513512.

It is not a de Polignac number, because 21531587 - 2¹⁰ = 21530563 is a prime.

It is a Duffinian number.

It is a zygodrome in base 11.

It is not an unprimeable number, because it can be changed into a prime (21531527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8162 + ... + 10472.

It is an arithmetic number, because the mean of its divisors is an integer number (1692384).

Almost surely, 2^21531587 is an apocalyptic number.

21531587 is a deficient number, since it is larger than the sum of its proper divisors (5546557).

21531587 is an equidigital number, since it uses as much as digits as its factorization.

21531587 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2351 (or 2329 counting only the distinct ones).

The product of its digits is 8400, while the sum is 32.

The square root of 21531587 is about 4640.2141114393. The cubic root of 21531587 is about 278.2009958889.

The spelling of 21531587 in words is "twenty-one million, five hundred thirty-one thousand, five hundred eighty-seven".