21997998 has 48 divisors (see below), whose sum is σ = 52324272. Its totient is φ = 6624000.

The previous prime is 21997981. The next prime is 21998027. The reversal of 21997998 is 89979912.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 47488 + ... + 47948.

It is an arithmetic number, because the mean of its divisors is an integer number (1090089).

Almost surely, 2^21997998 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21997998, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26162136).

21997998 is an abundant number, since it is smaller than the sum of its proper divisors (30326274).

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

21997998 is a wasteful number, since it uses less digits than its factorization.

21997998 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 721 (or 718 counting only the distinct ones).

The product of its digits is 734832, while the sum is 54.

The square root of 21997998 is about 4690.2023410510. The cubic root of 21997998 is about 280.1954332884.

The spelling of 21997998 in words is "twenty-one million, nine hundred ninety-seven thousand, nine hundred ninety-eight".