21504709 has 4 divisors (see below), whose sum is σ = 21962304. Its totient is φ = 21047116.

The previous prime is 21504647. The next prime is 21504727. The reversal of 21504709 is 90740512.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21504709 - 2¹⁵ = 21471941 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 (21504799) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 228727 + ... + 228820.

It is an arithmetic number, because the mean of its divisors is an integer number (5490576).

Almost surely, 2^21504709 is an apocalyptic number.

It is an amenable number.

21504709 is a deficient number, since it is larger than the sum of its proper divisors (457595).

21504709 is an equidigital number, since it uses as much as digits as its factorization.

21504709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 457594.

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21504709 is about 4637.3170044758. The cubic root of 21504709 is about 278.0851877365.

It can be divided in two parts, 2150 and 4709, that added together give a cube (6859 = 19³).

The spelling of 21504709 in words is "twenty-one million, five hundred four thousand, seven hundred nine".