21897864 has 80 divisors (see below), whose sum is σ = 62726400. Its totient is φ = 7134048.

The previous prime is 21897857. The next prime is 21897881. The reversal of 21897864 is 46879812.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 30097 + ... + 30815.

It is an arithmetic number, because the mean of its divisors is an integer number (784080).

Almost surely, 2^21897864 is an apocalyptic number.

21897864 is a gapful number since it is divisible by the number (24) 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 21897864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31363200).

21897864 is an abundant number, since it is smaller than the sum of its proper divisors (40828536).

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

21897864 is a wasteful number, since it uses less digits than its factorization.

21897864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 784 (or 771 counting only the distinct ones).

The product of its digits is 193536, while the sum is 45.

The square root of 21897864 is about 4679.5153595218. The cubic root of 21897864 is about 279.7696404642.

The spelling of 21897864 in words is "twenty-one million, eight hundred ninety-seven thousand, eight hundred sixty-four".