21087521 has 16 divisors (see below), whose sum is σ = 26659584. Its totient is φ = 16231104.

The previous prime is 21087491. The next prime is 21087529. The reversal of 21087521 is 12578012.

It is a cyclic number.

It is not a de Polignac number, because 21087521 - 2⁶ = 21087457 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21087529) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 236 + ... + 6498.

It is an arithmetic number, because the mean of its divisors is an integer number (1666224).

Almost surely, 2^21087521 is an apocalyptic number.

It is an amenable number.

21087521 is a deficient number, since it is larger than the sum of its proper divisors (5572063).

21087521 is a wasteful number, since it uses less digits than its factorization.

21087521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6320.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21087521 is about 4592.1150900212. The cubic root of 21087521 is about 276.2751622897.

The spelling of 21087521 in words is "twenty-one million, eighty-seven thousand, five hundred twenty-one".