21997744 has 30 divisors (see below), whose sum is σ = 45031220. Its totient is φ = 10381248.

The previous prime is 21997733. The next prime is 21997751. The reversal of 21997744 is 44779912.

It is a self number, because there is not a number n which added to its sum of digits gives 21997744.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 81642 + ... + 81910.

Almost surely, 2^21997744 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 21997744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22515610).

21997744 is an abundant number, since it is smaller than the sum of its proper divisors (23033476).

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

21997744 is an equidigital number, since it uses as much as digits as its factorization.

21997744 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 565 (or 290 counting only the distinct ones).

The product of its digits is 127008, while the sum is 43.

The square root of 21997744 is about 4690.1752632498. The cubic root of 21997744 is about 280.1943548582.

The spelling of 21997744 in words is "twenty-one million, nine hundred ninety-seven thousand, seven hundred forty-four".