21894721 has 4 divisors (see below), whose sum is σ = 22095700. Its totient is φ = 21693744.

The previous prime is 21894703. The next prime is 21894737. The reversal of 21894721 is 12749812.

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 16769025 + 5125696 = 4095^2 + 2264^2 .

It is a cyclic number.

It is not a de Polignac number, because 21894721 - 2¹⁷ = 21763649 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21894701) 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, 100326 + ... + 100543.

It is an arithmetic number, because the mean of its divisors is an integer number (5523925).

Almost surely, 2^21894721 is an apocalyptic number.

It is an amenable number.

21894721 is a deficient number, since it is larger than the sum of its proper divisors (200979).

21894721 is a wasteful number, since it uses less digits than its factorization.

21894721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 200978.

The product of its digits is 8064, while the sum is 34.

The square root of 21894721 is about 4679.1795220957. The cubic root of 21894721 is about 279.7562547134.

The spelling of 21894721 in words is "twenty-one million, eight hundred ninety-four thousand, seven hundred twenty-one".