21821947 has 4 divisors (see below), whose sum is σ = 24939376. Its totient is φ = 18704520.

The previous prime is 21821929. The next prime is 21821953. The reversal of 21821947 is 74912812.

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 21821947 - 2⁷ = 21821819 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21821927) by changing a digit.

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 in 3 ways as a sum of consecutive naturals, for example, 1558704 + ... + 1558717.

It is an arithmetic number, because the mean of its divisors is an integer number (6234844).

Almost surely, 2^21821947 is an apocalyptic number.

21821947 is a deficient number, since it is larger than the sum of its proper divisors (3117429).

21821947 is an equidigital number, since it uses as much as digits as its factorization.

21821947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3117428.

The product of its digits is 8064, while the sum is 34.

The square root of 21821947 is about 4671.3966862171. The cubic root of 21821947 is about 279.4459579997.

The spelling of 21821947 in words is "twenty-one million, eight hundred twenty-one thousand, nine hundred forty-seven".