21821747 has 4 divisors (see below), whose sum is σ = 22970280. Its totient is φ = 20673216.

The previous prime is 21821729. The next prime is 21821753. The reversal of 21821747 is 74712812.

It is a happy number.

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

It is not a de Polignac number, because 21821747 - 2¹⁴ = 21805363 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21821707) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 574238 + ... + 574275.

It is an arithmetic number, because the mean of its divisors is an integer number (5742570).

Almost surely, 2^21821747 is an apocalyptic number.

21821747 is a deficient number, since it is larger than the sum of its proper divisors (1148533).

21821747 is a wasteful number, since it uses less digits than its factorization.

21821747 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1148532.

The product of its digits is 6272, while the sum is 32.

The square root of 21821747 is about 4671.3752792941. The cubic root of 21821747 is about 279.4451042818.

The spelling of 21821747 in words is "twenty-one million, eight hundred twenty-one thousand, seven hundred forty-seven".