21811906 has 4 divisors (see below), whose sum is σ = 32717862. Its totient is φ = 10905952.

The previous prime is 21811891. The next prime is 21811913. The reversal of 21811906 is 60911812.

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 only one way, i.e., 21706281 + 105625 = 4659^2 + 325^2 .

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 5452975 + ... + 5452978.

Almost surely, 2^21811906 is an apocalyptic number.

21811906 is a deficient number, since it is larger than the sum of its proper divisors (10905956).

21811906 is a wasteful number, since it uses less digits than its factorization.

21811906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10905955.

The product of its (nonzero) digits is 864, while the sum is 28.

The square root of 21811906 is about 4670.3218304524. The cubic root of 21811906 is about 279.4030906464.

The spelling of 21811906 in words is "twenty-one million, eight hundred eleven thousand, nine hundred six".