21397860 has 144 divisors (see below), whose sum is σ = 72176832. Its totient is φ = 5088000.

The previous prime is 21397847. The next prime is 21397867. The reversal of 21397860 is 6879312.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (21397867) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 199927 + ... + 200033.

It is an arithmetic number, because the mean of its divisors is an integer number (501228).

Almost surely, 2^21397860 is an apocalyptic number.

21397860 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 21397860, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36088416).

21397860 is an abundant number, since it is smaller than the sum of its proper divisors (50778972).

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

21397860 is a wasteful number, since it uses less digits than its factorization.

21397860 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 234 (or 229 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 21397860 is about 4625.7820960352. The cubic root of 21397860 is about 277.6238551091.

It can be divided in two parts, 2139 and 7860, that added together give a palindrome (9999).

The spelling of 21397860 in words is "twenty-one million, three hundred ninety-seven thousand, eight hundred sixty".