21645440 has 64 divisors (see below), whose sum is σ = 53464320. Its totient is φ = 8371200.

The previous prime is 21645439. The next prime is 21645443. The reversal of 21645440 is 4454612.

It is a tau number, because it is divible by the number of its divisors (64).

It is not an unprimeable number, because it can be changed into a prime (21645443) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19295 + ... + 20385.

It is an arithmetic number, because the mean of its divisors is an integer number (835380).

Almost surely, 2^21645440 is an apocalyptic number.

21645440 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 21645440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26732160).

21645440 is an abundant number, since it is smaller than the sum of its proper divisors (31818880).

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

21645440 is a wasteful number, since it uses less digits than its factorization.

21645440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1141 (or 1129 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 26.

The square root of 21645440 is about 4652.4660127722. The cubic root of 21645440 is about 278.6904837845.

The spelling of 21645440 in words is "twenty-one million, six hundred forty-five thousand, four hundred forty".