21906447 has 4 divisors (see below), whose sum is σ = 29208600. Its totient is φ = 14604296.

The previous prime is 21906413. The next prime is 21906461. The reversal of 21906447 is 74460912.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21906447 - 2¹⁸ = 21644303 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21906407) 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 in 3 ways as a sum of consecutive naturals, for example, 3651072 + ... + 3651077.

It is an arithmetic number, because the mean of its divisors is an integer number (7302150).

Almost surely, 2^21906447 is an apocalyptic number.

21906447 is a deficient number, since it is larger than the sum of its proper divisors (7302153).

21906447 is an equidigital number, since it uses as much as digits as its factorization.

21906447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7302152.

The product of its (nonzero) digits is 12096, while the sum is 33.

The square root of 21906447 is about 4680.4323518239. The cubic root of 21906447 is about 279.8061881562.

The spelling of 21906447 in words is "twenty-one million, nine hundred six thousand, four hundred forty-seven".