21815906 has 8 divisors (see below), whose sum is σ = 37398720. Its totient is φ = 9349668.

The previous prime is 21815897. The next prime is 21815939. The reversal of 21815906 is 60951812.

It is a sphenic number, since it is the product of 3 distinct primes.

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 in 3 ways as a sum of consecutive naturals, for example, 779126 + ... + 779153.

It is an arithmetic number, because the mean of its divisors is an integer number (4674840).

Almost surely, 2^21815906 is an apocalyptic number.

21815906 is a deficient number, since it is larger than the sum of its proper divisors (15582814).

21815906 is a wasteful number, since it uses less digits than its factorization.

21815906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1558288.

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 21815906 is about 4670.7500468340. The cubic root of 21815906 is about 279.4201691485.

The spelling of 21815906 in words is "twenty-one million, eight hundred fifteen thousand, nine hundred six".