21605440 has 56 divisors (see below), whose sum is σ = 52011072. Its totient is φ = 8547840.

The previous prime is 21605429. The next prime is 21605459. The reversal of 21605440 is 4450612.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 33925 + ... + 34555.

Almost surely, 2^21605440 is an apocalyptic number.

21605440 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 21605440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26005536).

21605440 is an abundant number, since it is smaller than the sum of its proper divisors (30405632).

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

21605440 is a wasteful number, since it uses less digits than its factorization.

21605440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 755 (or 745 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 22.

The square root of 21605440 is about 4648.1652294212. The cubic root of 21605440 is about 278.5187079092.

The spelling of 21605440 in words is "twenty-one million, six hundred five thousand, four hundred forty".