21043764 has 72 divisors (see below), whose sum is σ = 61414080. Its totient is φ = 5951232.

The previous prime is 21043753. The next prime is 21043793. The reversal of 21043764 is 46734012.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 28107 + ... + 28845.

Almost surely, 2^21043764 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21043764, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30707040).

21043764 is an abundant number, since it is smaller than the sum of its proper divisors (40370316).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21043764 is a wasteful number, since it uses less digits than its factorization.

21043764 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 869 (or 864 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 27.

The square root of 21043764 is about 4587.3482536210. The cubic root of 21043764 is about 276.0839379230.

Adding to 21043764 its reverse (46734012), we get a palindrome (67777776).

The spelling of 21043764 in words is "twenty-one million, forty-three thousand, seven hundred sixty-four".