21640800 has 144 divisors (see below), whose sum is σ = 71995392. Its totient is φ = 5644800.

The previous prime is 21640789. The next prime is 21640811. The reversal of 21640800 is 804612.

21640800 = T₇₄₅ + T₇₄₆ + ... + T₈₁₅.

It is an interprime number because it is at equal distance from previous prime (21640789) and next prime (21640811).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 170337 + ... + 170463.

It is an arithmetic number, because the mean of its divisors is an integer number (499968).

Almost surely, 2^21640800 is an apocalyptic number.

21640800 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 21640800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35997696).

21640800 is an abundant number, since it is smaller than the sum of its proper divisors (50354592).

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

21640800 is a wasteful number, since it uses less digits than its factorization.

21640800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 221 (or 208 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 21640800 is about 4651.9673257666. The cubic root of 21640800 is about 278.6705686391.

The spelling of 21640800 in words is "twenty-one million, six hundred forty thousand, eight hundred".