21285009 has 6 divisors (see below), whose sum is σ = 30745026. Its totient is φ = 14190000.

The previous prime is 21285007. The next prime is 21285013. The reversal of 21285009 is 90058212.

It can be written as a sum of positive squares in only one way, i.e., 15233409 + 6051600 = 3903^2 + 2460^2 .

It is not a de Polignac number, because 21285009 - 2¹ = 21285007 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21285007) 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, 1182492 + ... + 1182509.

It is an arithmetic number, because the mean of its divisors is an integer number (5124171).

Almost surely, 2^21285009 is an apocalyptic number.

It is an amenable number.

21285009 is a deficient number, since it is larger than the sum of its proper divisors (9460017).

21285009 is a wasteful number, since it uses less digits than its factorization.

21285009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2365007 (or 2365004 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 21285009 is about 4613.5679251529. The cubic root of 21285009 is about 277.1349375359.

The spelling of 21285009 in words is "twenty-one million, two hundred eighty-five thousand, nine".