21756789 has 8 divisors (see below), whose sum is σ = 32232320. Its totient is φ = 14504508.

The previous prime is 21756769. The next prime is 21756799. The reversal of 21756789 is 98765712.

21756789 is a `hidden beast` number, since 2 + 1 + 7 + 567 + 89 = 666.

It is not a de Polignac number, because 21756789 - 2¹¹ = 21754741 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 (21756769) 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 7 ways as a sum of consecutive naturals, for example, 402877 + ... + 402930.

It is an arithmetic number, because the mean of its divisors is an integer number (4029040).

Almost surely, 2^21756789 is an apocalyptic number.

It is an amenable number.

21756789 is a deficient number, since it is larger than the sum of its proper divisors (10475531).

21756789 is an equidigital number, since it uses as much as digits as its factorization.

21756789 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 805816 (or 805810 counting only the distinct ones).

The product of its digits is 211680, while the sum is 45.

The square root of 21756789 is about 4664.4173269552. The cubic root of 21756789 is about 279.1675488005.

The spelling of 21756789 in words is "twenty-one million, seven hundred fifty-six thousand, seven hundred eighty-nine".