21909889 has 4 divisors (see below), whose sum is σ = 23198724. Its totient is φ = 20621056.

The previous prime is 21909887. The next prime is 21909911. The reversal of 21909889 is 98890912.

It is a happy number.

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 7884864 + 14025025 = 2808^2 + 3745^2 .

It is a cyclic number.

It is not a de Polignac number, because 21909889 - 2¹ = 21909887 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21909887) 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, 644392 + ... + 644425.

It is an arithmetic number, because the mean of its divisors is an integer number (5799681).

Almost surely, 2^21909889 is an apocalyptic number.

It is an amenable number.

21909889 is a deficient number, since it is larger than the sum of its proper divisors (1288835).

21909889 is a wasteful number, since it uses less digits than its factorization.

21909889 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1288834.

The product of its (nonzero) digits is 93312, while the sum is 46.

The square root of 21909889 is about 4680.8000384550. The cubic root of 21909889 is about 279.8208420229.

The spelling of 21909889 in words is "twenty-one million, nine hundred nine thousand, eight hundred eighty-nine".