21012539 has 8 divisors (see below), whose sum is σ = 21706272. Its totient is φ = 20329920.

The previous prime is 21012533. The next prime is 21012569. The reversal of 21012539 is 93521012.

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 21012539 - 2⁸ = 21012283 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21012533) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1154 + ... + 6584.

It is an arithmetic number, because the mean of its divisors is an integer number (2713284).

Almost surely, 2^21012539 is an apocalyptic number.

21012539 is a deficient number, since it is larger than the sum of its proper divisors (693733).

21012539 is an equidigital number, since it uses as much as digits as its factorization.

21012539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5557.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21012539 is about 4583.9436078556. The cubic root of 21012539 is about 275.9473180622.

It can be divided in two parts, 2 and 1012539, that multiplied together give a triangular number (2025078 = T₂₀₁₂).

The spelling of 21012539 in words is "twenty-one million, twelve thousand, five hundred thirty-nine".