21840780 has 48 divisors (see below), whose sum is σ = 65860704. Its totient is φ = 5376000.

The previous prime is 21840773. The next prime is 21840787. The reversal of 21840780 is 8704812.

It is an interprime number because it is at equal distance from previous prime (21840773) and next prime (21840787).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is not an unprimeable number, because it can be changed into a prime (21840787) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 13221 + ... + 14780.

It is an arithmetic number, because the mean of its divisors is an integer number (1372098).

Almost surely, 2^21840780 is an apocalyptic number.

21840780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21840780 is an abundant number, since it is smaller than the sum of its proper divisors (44019924).

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

21840780 is a wasteful number, since it uses less digits than its factorization.

21840780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28026 (or 28024 counting only the distinct ones).

The product of its (nonzero) digits is 3584, while the sum is 30.

The square root of 21840780 is about 4673.4120297701. The cubic root of 21840780 is about 279.5263249879.

The spelling of 21840780 in words is "twenty-one million, eight hundred forty thousand, seven hundred eighty".