21748729 has 4 divisors (see below), whose sum is σ = 23028084. Its totient is φ = 20469376.

The previous prime is 21748717. The next prime is 21748747. The reversal of 21748729 is 92784712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7573504 + 14175225 = 2752^2 + 3765^2 .

It is a cyclic number.

It is not a de Polignac number, because 21748729 - 2⁵ = 21748697 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21748691 and 21748700.

It is not an unprimeable number, because it can be changed into a prime (21748789) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 639652 + ... + 639685.

It is an arithmetic number, because the mean of its divisors is an integer number (5757021).

Almost surely, 2^21748729 is an apocalyptic number.

It is an amenable number.

21748729 is a deficient number, since it is larger than the sum of its proper divisors (1279355).

21748729 is a wasteful number, since it uses less digits than its factorization.

21748729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1279354.

The product of its digits is 56448, while the sum is 40.

The square root of 21748729 is about 4663.5532590504. The cubic root of 21748729 is about 279.1330711583.

The spelling of 21748729 in words is "twenty-one million, seven hundred forty-eight thousand, seven hundred twenty-nine".