21757906 has 4 divisors (see below), whose sum is σ = 32636862. Its totient is φ = 10878952.

The previous prime is 21757873. The next prime is 21757951. The reversal of 21757906 is 60975712.

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., 21077281 + 680625 = 4591^2 + 825^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5439475 + ... + 5439478.

Almost surely, 2^21757906 is an apocalyptic number.

21757906 is a deficient number, since it is larger than the sum of its proper divisors (10878956).

21757906 is a wasteful number, since it uses less digits than its factorization.

21757906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10878955.

The product of its (nonzero) digits is 26460, while the sum is 37.

The square root of 21757906 is about 4664.5370617029. The cubic root of 21757906 is about 279.1723262336.

The spelling of 21757906 in words is "twenty-one million, seven hundred fifty-seven thousand, nine hundred six".