21840820 has 12 divisors (see below), whose sum is σ = 45865764. Its totient is φ = 8736320.

The previous prime is 21840817. The next prime is 21840829. The reversal of 21840820 is 2804812.

It can be written as a sum of positive squares in 2 ways, for example, as 17405584 + 4435236 = 4172^2 + 2106^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21840829) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 546001 + ... + 546040.

It is an arithmetic number, because the mean of its divisors is an integer number (3822147).

Almost surely, 2^21840820 is an apocalyptic number.

21840820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21840820 is an abundant number, since it is smaller than the sum of its proper divisors (24024944).

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

21840820 is a wasteful number, since it uses less digits than its factorization.

21840820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1092050 (or 1092048 counting only the distinct ones).

The product of its (nonzero) digits is 1024, while the sum is 25.

The square root of 21840820 is about 4673.4163092967. The cubic root of 21840820 is about 279.5264956326.

The spelling of 21840820 in words is "twenty-one million, eight hundred forty thousand, eight hundred twenty".