21997220 has 48 divisors (see below), whose sum is σ = 53561088. Its totient is φ = 7432320.

The previous prime is 21997219. The next prime is 21997237. The reversal of 21997220 is 2279912.

It is a Smith number, since the sum of its digits (32) coincides with the sum of the digits of its prime factors.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8834 + ... + 11046.

It is an arithmetic number, because the mean of its divisors is an integer number (1115856).

Almost surely, 2^21997220 is an apocalyptic number.

21997220 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 21997220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26780544).

21997220 is an abundant number, since it is smaller than the sum of its proper divisors (31563868).

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

21997220 is a wasteful number, since it uses less digits than its factorization.

21997220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2300 (or 2298 counting only the distinct ones).

The product of its (nonzero) digits is 4536, while the sum is 32.

The square root of 21997220 is about 4690.1194014652. The cubic root of 21997220 is about 280.1921300391.

The spelling of 21997220 in words is "twenty-one million, nine hundred ninety-seven thousand, two hundred twenty".