21990816 has 72 divisors (see below), whose sum is σ = 64717380. Its totient is φ = 7074816.

The previous prime is 21990799. The next prime is 21990821. The reversal of 21990816 is 61809912.

It can be written as a sum of positive squares in 2 ways, for example, as 21344400 + 646416 = 4620^2 + 804^2 .

It is a tau number, because it is divible by the number of its divisors (72).

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

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7036 + ... + 9668.

Almost surely, 2^21990816 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21990816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32358690).

21990816 is an abundant number, since it is smaller than the sum of its proper divisors (42726564).

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

21990816 is a wasteful number, since it uses less digits than its factorization.

21990816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2678 (or 2667 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 36.

The square root of 21990816 is about 4689.4366399387. The cubic root of 21990816 is about 280.1649368368.

The spelling of 21990816 in words is "twenty-one million, nine hundred ninety thousand, eight hundred sixteen".