21743821 has 12 divisors (see below), whose sum is σ = 24246432. Its totient is φ = 19481000.

The previous prime is 21743807. The next prime is 21743831. The reversal of 21743821 is 12834712.

It is not a de Polignac number, because 21743821 - 2⁵ = 21743789 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21743821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21743831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7326 + ... + 9856.

It is an arithmetic number, because the mean of its divisors is an integer number (2020536).

Almost surely, 2^21743821 is an apocalyptic number.

It is an amenable number.

21743821 is a deficient number, since it is larger than the sum of its proper divisors (2502611).

21743821 is a wasteful number, since it uses less digits than its factorization.

21743821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2624 (or 2613 counting only the distinct ones).

The product of its digits is 2688, while the sum is 28.

The square root of 21743821 is about 4663.0270211527. The cubic root of 21743821 is about 279.1120724112.

It can be divided in two parts, 2174 and 3821, that added together give a palindrome (5995).

The spelling of 21743821 in words is "twenty-one million, seven hundred forty-three thousand, eight hundred twenty-one".