21015009 has 12 divisors (see below), whose sum is σ = 32140836. Its totient is φ = 13185792.

The previous prime is 21014999. The next prime is 21015011. The reversal of 21015009 is 90051012.

It can be written as a sum of positive squares in 2 ways, for example, as 10419984 + 10595025 = 3228^2 + 3255^2 .

It is not a de Polignac number, because 21015009 - 2⁸ = 21014753 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21014982 and 21015000.

It is not an unprimeable number, because it can be changed into a prime (21015079) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 68524 + ... + 68829.

It is an arithmetic number, because the mean of its divisors is an integer number (2678403).

Almost surely, 2^21015009 is an apocalyptic number.

It is an amenable number.

21015009 is a deficient number, since it is larger than the sum of its proper divisors (11125827).

21015009 is a wasteful number, since it uses less digits than its factorization.

21015009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137376 (or 137373 counting only the distinct ones).

The product of its (nonzero) digits is 90, while the sum is 18.

The square root of 21015009 is about 4584.2130186107. The cubic root of 21015009 is about 275.9581300695.

The spelling of 21015009 in words is "twenty-one million, fifteen thousand, nine".