21531749 has 8 divisors (see below), whose sum is σ = 22567680. Its totient is φ = 20504176.

The previous prime is 21531739. The next prime is 21531773. The reversal of 21531749 is 94713512.

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 21531749 - 2⁴ = 21531733 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531709) 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, 3539 + ... + 7455.

It is an arithmetic number, because the mean of its divisors is an integer number (2820960).

Almost surely, 2^21531749 is an apocalyptic number.

It is an amenable number.

21531749 is a deficient number, since it is larger than the sum of its proper divisors (1035931).

21531749 is a wasteful number, since it uses less digits than its factorization.

21531749 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4179.

The product of its digits is 7560, while the sum is 32.

The square root of 21531749 is about 4640.2315674975. The cubic root of 21531749 is about 278.2016935994.

The spelling of 21531749 in words is "twenty-one million, five hundred thirty-one thousand, seven hundred forty-nine".