21725906 has 4 divisors (see below), whose sum is σ = 32588862. Its totient is φ = 10862952.

The previous prime is 21725903. The next prime is 21725933. The reversal of 21725906 is 60952712.

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., 21242881 + 483025 = 4609^2 + 695^2 .

It is not an unprimeable number, because it can be changed into a prime (21725903) by changing a digit.

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, 5431475 + ... + 5431478.

Almost surely, 2^21725906 is an apocalyptic number.

21725906 is a deficient number, since it is larger than the sum of its proper divisors (10862956).

21725906 is a wasteful number, since it uses less digits than its factorization.

21725906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10862955.

The product of its (nonzero) digits is 7560, while the sum is 32.

The square root of 21725906 is about 4661.1056628229. The cubic root of 21725906 is about 279.0353967329.

The spelling of 21725906 in words is "twenty-one million, seven hundred twenty-five thousand, nine hundred six".