21645900 has 72 divisors (see below), whose sum is σ = 69596240. Its totient is φ = 5771520.

The previous prime is 21645881. The next prime is 21645901. The reversal of 21645900 is 954612.

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

It is not an unprimeable number, because it can be changed into a prime (21645901) 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, 1309 + ... + 6708.

Almost surely, 2^21645900 is an apocalyptic number.

21645900 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 21645900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34798120).

21645900 is an abundant number, since it is smaller than the sum of its proper divisors (47950340).

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

21645900 is a wasteful number, since it uses less digits than its factorization.

21645900 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8040 (or 8027 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21645900 is about 4652.5154486579. The cubic root of 21645900 is about 278.6924579758.

The spelling of 21645900 in words is "twenty-one million, six hundred forty-five thousand, nine hundred".