21798720 has 210 divisors, whose sum is σ = 80307942. Its totient is φ = 5612544.

The previous prime is 21798703. The next prime is 21798727. The reversal of 21798720 is 2789712.

It can be written as a sum of positive squares in 3 ways, for example, as 2509056 + 19289664 = 1584^2 + 4392^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21798727) 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 29 ways as a sum of consecutive naturals, for example, 751666 + ... + 751694.

Almost surely, 2^21798720 is an apocalyptic number.

21798720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21798720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40153971).

21798720 is an abundant number, since it is smaller than the sum of its proper divisors (58509222).

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

21798720 is an equidigital number, since it uses as much as digits as its factorization.

21798720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 87 (or 39 counting only the distinct ones).

The product of its (nonzero) digits is 14112, while the sum is 36.

The square root of 21798720 is about 4668.9099370196. The cubic root of 21798720 is about 279.3467765732.

The spelling of 21798720 in words is "twenty-one million, seven hundred ninety-eight thousand, seven hundred twenty".