21990720 has 56 divisors (see below), whose sum is σ = 69823584. Its totient is φ = 5863936.

The previous prime is 21990713. The next prime is 21990721. The reversal of 21990720 is 2709912.

It is a super-2 number, since 2×21990720² = 967183532236800, which contains 22 as substring.

It is a hoax number, since the sum of its digits (30) coincides with the sum of the digits of its distinct prime factors.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21990721) 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 7 ways as a sum of consecutive naturals, for example, 10494 + ... + 12413.

Almost surely, 2^21990720 is an apocalyptic number.

21990720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21990720 is an abundant number, since it is smaller than the sum of its proper divisors (47832864).

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

21990720 is a wasteful number, since it uses less digits than its factorization.

21990720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22927 (or 22917 counting only the distinct ones).

The product of its (nonzero) digits is 2268, while the sum is 30.

The square root of 21990720 is about 4689.4264041565. The cubic root of 21990720 is about 280.1645291534.

The spelling of 21990720 in words is "twenty-one million, nine hundred ninety thousand, seven hundred twenty".