21087009 has 6 divisors (see below), whose sum is σ = 30459026. Its totient is φ = 14058000.

The previous prime is 21086981. The next prime is 21087019. The reversal of 21087009 is 90078012.

It can be written as a sum of positive squares in only one way, i.e., 20277009 + 810000 = 4503^2 + 900^2 .

It is not a de Polignac number, because 21087009 - 2⁸ = 21086753 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21087019) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1171492 + ... + 1171509.

Almost surely, 2^21087009 is an apocalyptic number.

It is an amenable number.

21087009 is a deficient number, since it is larger than the sum of its proper divisors (9372017).

21087009 is a wasteful number, since it uses less digits than its factorization.

21087009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2343007 (or 2343004 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 27.

The square root of 21087009 is about 4592.0593419511. The cubic root of 21087009 is about 276.2729263065.

The spelling of 21087009 in words is "twenty-one million, eighty-seven thousand, nine".