21018009 has 8 divisors (see below), whose sum is σ = 29499040. Its totient is φ = 13274496.

The previous prime is 21017993. The next prime is 21018043. The reversal of 21018009 is 90081012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21018009 - 2⁴ = 21017993 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21018079) 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 7 ways as a sum of consecutive naturals, for example, 184312 + ... + 184425.

It is an arithmetic number, because the mean of its divisors is an integer number (3687380).

Almost surely, 2^21018009 is an apocalyptic number.

It is an amenable number.

21018009 is a deficient number, since it is larger than the sum of its proper divisors (8481031).

21018009 is a wasteful number, since it uses less digits than its factorization.

21018009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 368759.

The product of its (nonzero) digits is 144, while the sum is 21.

The square root of 21018009 is about 4584.5402168593. The cubic root of 21018009 is about 275.9712609227.

The spelling of 21018009 in words is "twenty-one million, eighteen thousand, nine".