21657900 has 72 divisors (see below), whose sum is σ = 68370624. Its totient is φ = 5249600.

The previous prime is 21657877. The next prime is 21657901. The reversal of 21657900 is 975612.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is not an unprimeable number, because it can be changed into a prime (21657901) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 19 + ... + 6581.

It is an arithmetic number, because the mean of its divisors is an integer number (949592).

Almost surely, 2^21657900 is an apocalyptic number.

21657900 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 21657900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34185312).

21657900 is an abundant number, since it is smaller than the sum of its proper divisors (46712724).

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

21657900 is a wasteful number, since it uses less digits than its factorization.

21657900 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6591 (or 6584 counting only the distinct ones).

The product of its (nonzero) digits is 3780, while the sum is 30.

The square root of 21657900 is about 4653.8048949220. The cubic root of 21657900 is about 278.7439487382.

The spelling of 21657900 in words is "twenty-one million, six hundred fifty-seven thousand, nine hundred".