21013509 has 8 divisors (see below), whose sum is σ = 30565152. Its totient is φ = 12735440.

The previous prime is 21013507. The next prime is 21013511. The reversal of 21013509 is 90531012.

It is an interprime number because it is at equal distance from previous prime (21013507) and next prime (21013511).

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

It is a cyclic number.

It is not a de Polignac number, because 21013509 - 2¹ = 21013507 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21013501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 318354 + ... + 318419.

It is an arithmetic number, because the mean of its divisors is an integer number (3820644).

Almost surely, 2^21013509 is an apocalyptic number.

It is an amenable number.

21013509 is a deficient number, since it is larger than the sum of its proper divisors (9551643).

21013509 is a wasteful number, since it uses less digits than its factorization.

21013509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 636787.

The product of its (nonzero) digits is 270, while the sum is 21.

The square root of 21013509 is about 4584.0494107285. The cubic root of 21013509 is about 275.9515641742.

The spelling of 21013509 in words is "twenty-one million, thirteen thousand, five hundred nine".