21172947 has 4 divisors (see below), whose sum is σ = 28230600. Its totient is φ = 14115296.

The previous prime is 21172927. The next prime is 21172961. The reversal of 21172947 is 74927112.

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 21172947 - 2⁶ = 21172883 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21172927) 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, 3528822 + ... + 3528827.

It is an arithmetic number, because the mean of its divisors is an integer number (7057650).

Almost surely, 2^21172947 is an apocalyptic number.

21172947 is a deficient number, since it is larger than the sum of its proper divisors (7057653).

21172947 is an equidigital number, since it uses as much as digits as its factorization.

21172947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7057652.

The product of its digits is 7056, while the sum is 33.

The square root of 21172947 is about 4601.4070674088. The cubic root of 21172947 is about 276.6477251915.

The spelling of 21172947 in words is "twenty-one million, one hundred seventy-two thousand, nine hundred forty-seven".