21732821 has 16 divisors (see below), whose sum is σ = 24364800. Its totient is φ = 19219200.

The previous prime is 21732811. The next prime is 21732833. The reversal of 21732821 is 12823712.

It is not a de Polignac number, because 21732821 - 2¹⁴ = 21716437 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21732811) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 77201 + ... + 77481.

It is an arithmetic number, because the mean of its divisors is an integer number (1522800).

Almost surely, 2^21732821 is an apocalyptic number.

It is an amenable number.

21732821 is a deficient number, since it is larger than the sum of its proper divisors (2631979).

21732821 is a wasteful number, since it uses less digits than its factorization.

21732821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 460.

The product of its digits is 1344, while the sum is 26.

The square root of 21732821 is about 4661.8473805992. The cubic root of 21732821 is about 279.0649977246.

It can be divided in two parts, 2173 and 2821, that added together give a palindrome (4994).

The spelling of 21732821 in words is "twenty-one million, seven hundred thirty-two thousand, eight hundred twenty-one".