21997872 has 80 divisors (see below), whose sum is σ = 68016480. Its totient is φ = 6766848.

The previous prime is 21997861. The next prime is 21997931. The reversal of 21997872 is 27879912.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3658 + ... + 7574.

It is an arithmetic number, because the mean of its divisors is an integer number (850206).

Almost surely, 2^21997872 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 21997872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34008240).

21997872 is an abundant number, since it is smaller than the sum of its proper divisors (46018608).

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

21997872 is a wasteful number, since it uses less digits than its factorization.

21997872 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3947 (or 3935 counting only the distinct ones).

The product of its digits is 127008, while the sum is 45.

The square root of 21997872 is about 4690.1889087754. The cubic root of 21997872 is about 280.1948983201.

The spelling of 21997872 in words is "twenty-one million, nine hundred ninety-seven thousand, eight hundred seventy-two".