21909073 has 4 divisors (see below), whose sum is σ = 23197860. Its totient is φ = 20620288.

The previous prime is 21909029. The next prime is 21909077. The reversal of 21909073 is 37090912.

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 13046544 + 8862529 = 3612^2 + 2977^2 .

It is a cyclic number.

It is not a de Polignac number, because 21909073 - 2⁹ = 21908561 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21909077) 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, 644368 + ... + 644401.

It is an arithmetic number, because the mean of its divisors is an integer number (5799465).

Almost surely, 2^21909073 is an apocalyptic number.

It is an amenable number.

21909073 is a deficient number, since it is larger than the sum of its proper divisors (1288787).

21909073 is a wasteful number, since it uses less digits than its factorization.

21909073 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1288786.

The product of its (nonzero) digits is 3402, while the sum is 31.

The square root of 21909073 is about 4680.7128730568. The cubic root of 21909073 is about 279.8173681480.

Adding to 21909073 its reverse (37090912), we get a palindrome (58999985).

The spelling of 21909073 in words is "twenty-one million, nine hundred nine thousand, seventy-three".