21788240 has 20 divisors (see below), whose sum is σ = 50657844. Its totient is φ = 8715264.

The previous prime is 21788233. The next prime is 21788293. The reversal of 21788240 is 4288712.

It can be written as a sum of positive squares in 2 ways, for example, as 7011904 + 14776336 = 2648^2 + 3844^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a zygodrome in base 9.

It is a junction number, because it is equal to n+sod(n) for n = 21788197 and 21788206.

It is a congruent number.

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, 136097 + ... + 136256.

Almost surely, 2^21788240 is an apocalyptic number.

21788240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21788240 is an abundant number, since it is smaller than the sum of its proper divisors (28869604).

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

21788240 is a wasteful number, since it uses less digits than its factorization.

21788240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 272366 (or 272360 counting only the distinct ones).

The product of its (nonzero) digits is 7168, while the sum is 32.

The square root of 21788240 is about 4667.7874844513. The cubic root of 21788240 is about 279.3020029428.

The spelling of 21788240 in words is "twenty-one million, seven hundred eighty-eight thousand, two hundred forty".