21909806 has 4 divisors (see below), whose sum is σ = 32864712. Its totient is φ = 10954902.

The previous prime is 21909799. The next prime is 21909817. The reversal of 21909806 is 60890912.

It is a semiprime because it is the product of two primes.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5477450 + ... + 5477453.

It is an arithmetic number, because the mean of its divisors is an integer number (8216178).

Almost surely, 2^21909806 is an apocalyptic number.

21909806 is a deficient number, since it is larger than the sum of its proper divisors (10954906).

21909806 is a wasteful number, since it uses less digits than its factorization.

21909806 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10954905.

The product of its (nonzero) digits is 7776, while the sum is 35.

The square root of 21909806 is about 4680.7911724408. The cubic root of 21909806 is about 279.8204886793.

The spelling of 21909806 in words is "twenty-one million, nine hundred nine thousand, eight hundred six".