21788840 has 16 divisors (see below), whose sum is σ = 49024980. Its totient is φ = 8715520.

The previous prime is 21788827. The next prime is 21788857. The reversal of 21788840 is 4888712.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 20484676 + 1304164 = 4526^2 + 1142^2 .

It is a super-3 number, since 3×21788840³ (a number of 23 digits) contains 333 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21788794 and 21788803.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 272321 + ... + 272400.

Almost surely, 2^21788840 is an apocalyptic number.

21788840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21788840 is an abundant number, since it is smaller than the sum of its proper divisors (27236140).

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

21788840 is a wasteful number, since it uses less digits than its factorization.

21788840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 544732 (or 544728 counting only the distinct ones).

The product of its (nonzero) digits is 28672, while the sum is 38.

The square root of 21788840 is about 4667.8517542870. The cubic root of 21788840 is about 279.3045667060.

The spelling of 21788840 in words is "twenty-one million, seven hundred eighty-eight thousand, eight hundred forty".