21790720 has 128 divisors (see below), whose sum is σ = 62913600. Its totient is φ = 7077888.

The previous prime is 21790711. The next prime is 21790801. The reversal of 21790720 is 2709712.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1146871 + ... + 1146889.

Almost surely, 2^21790720 is an apocalyptic number.

21790720 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 21790720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31456800).

21790720 is an abundant number, since it is smaller than the sum of its proper divisors (41122880).

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

21790720 is an frugal number, since it uses more digits than its factorization.

21790720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 61 (or 33 counting only the distinct ones).

The product of its (nonzero) digits is 1764, while the sum is 28.

The square root of 21790720 is about 4668.0531273755. The cubic root of 21790720 is about 279.3125995260.

The spelling of 21790720 in words is "twenty-one million, seven hundred ninety thousand, seven hundred twenty".