21747745 has 4 divisors (see below), whose sum is σ = 26097300. Its totient is φ = 17398192.

The previous prime is 21747727. The next prime is 21747751. The reversal of 21747745 is 54774712.

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 4032064 + 17715681 = 2008^2 + 4209^2 .

It is a cyclic number.

It is not a de Polignac number, because 21747745 - 2⁷ = 21747617 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2174770 + ... + 2174779.

It is an arithmetic number, because the mean of its divisors is an integer number (6524325).

Almost surely, 2^21747745 is an apocalyptic number.

It is an amenable number.

21747745 is a deficient number, since it is larger than the sum of its proper divisors (4349555).

21747745 is an equidigital number, since it uses as much as digits as its factorization.

21747745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4349554.

The product of its digits is 54880, while the sum is 37.

The square root of 21747745 is about 4663.4477589011. The cubic root of 21747745 is about 279.1288613938.

The spelling of 21747745 in words is "twenty-one million, seven hundred forty-seven thousand, seven hundred forty-five".