21397500 has 120 divisors (see below), whose sum is σ = 69540240. Its totient is φ = 5688000.

The previous prime is 21397489. The next prime is 21397501. The reversal of 21397500 is 579312.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21397501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 67342 + ... + 67658.

It is an arithmetic number, because the mean of its divisors is an integer number (579502).

Almost surely, 2^21397500 is an apocalyptic number.

21397500 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 21397500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34770120).

21397500 is an abundant number, since it is smaller than the sum of its proper divisors (48142740).

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

21397500 is a wasteful number, since it uses less digits than its factorization.

21397500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 350 (or 327 counting only the distinct ones).

The product of its (nonzero) digits is 1890, while the sum is 27.

The square root of 21397500 is about 4625.7431835328. The cubic root of 21397500 is about 277.6222981754.

The spelling of 21397500 in words is "twenty-one million, three hundred ninety-seven thousand, five hundred".