21840745 has 16 divisors (see below), whose sum is σ = 26940240. Its totient is φ = 16992000.

The previous prime is 21840743. The next prime is 21840751. The reversal of 21840745 is 54704812.

It can be written as a sum of positive squares in 8 ways, for example, as 1734489 + 20106256 = 1317^2 + 4484^2 .

It is not a de Polignac number, because 21840745 - 2¹ = 21840743 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21840743) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 30451 + ... + 31159.

It is an arithmetic number, because the mean of its divisors is an integer number (1683765).

Almost surely, 2^21840745 is an apocalyptic number.

It is an amenable number.

21840745 is a deficient number, since it is larger than the sum of its proper divisors (5099495).

21840745 is a wasteful number, since it uses less digits than its factorization.

21840745 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 876.

The product of its (nonzero) digits is 8960, while the sum is 31.

The square root of 21840745 is about 4673.4082851812. The cubic root of 21840745 is about 279.5261756735.

The spelling of 21840745 in words is "twenty-one million, eight hundred forty thousand, seven hundred forty-five".