21756806 has 4 divisors (see below), whose sum is σ = 32635212. Its totient is φ = 10878402.

The previous prime is 21756803. The next prime is 21756811. The reversal of 21756806 is 60865712.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21756803) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5439200 + ... + 5439203.

It is an arithmetic number, because the mean of its divisors is an integer number (8158803).

Almost surely, 2^21756806 is an apocalyptic number.

21756806 is a deficient number, since it is larger than the sum of its proper divisors (10878406).

21756806 is a wasteful number, since it uses less digits than its factorization.

21756806 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10878405.

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 21756806 is about 4664.4191492618. The cubic root of 21756806 is about 279.1676215111.

The spelling of 21756806 in words is "twenty-one million, seven hundred fifty-six thousand, eight hundred six".