21889721 has 12 divisors (see below), whose sum is σ = 26572032. Its totient is φ = 17945928.

The previous prime is 21889717. The next prime is 21889741. The reversal of 21889721 is 12798812.

It is not a de Polignac number, because 21889721 - 2² = 21889717 is a prime.

It is a Smith number, since the sum of its digits (38) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21889741) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 8585 + ... + 10838.

It is an arithmetic number, because the mean of its divisors is an integer number (2214336).

Almost surely, 2^21889721 is an apocalyptic number.

It is an amenable number.

21889721 is a deficient number, since it is larger than the sum of its proper divisors (4682311).

21889721 is a wasteful number, since it uses less digits than its factorization.

21889721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19460 (or 19453 counting only the distinct ones).

The product of its digits is 16128, while the sum is 38.

The square root of 21889721 is about 4678.6452098872. The cubic root of 21889721 is about 279.7349575285.

Subtracting from 21889721 its reverse (12798812), we obtain a palindrome (9090909).

The spelling of 21889721 in words is "twenty-one million, eight hundred eighty-nine thousand, seven hundred twenty-one".