21428640 has 144 divisors (see below), whose sum is σ = 76422528. Its totient is φ = 5457408.

The previous prime is 21428621. The next prime is 21428681. The reversal of 21428640 is 4682412.

21428640 is a `hidden beast` number, since 2 + 14 + 2 + 8 + 640 = 666.

It is a tau number, because it is divible by the number of its divisors (144).

It is a super-2 number, since 2×21428640² = 918373224499200, which contains 22 as substring.

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, 32797 + ... + 33443.

It is an arithmetic number, because the mean of its divisors is an integer number (530712).

Almost surely, 2^21428640 is an apocalyptic number.

21428640 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 21428640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38211264).

21428640 is an abundant number, since it is smaller than the sum of its proper divisors (54993888).

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

21428640 is a wasteful number, since it uses less digits than its factorization.

21428640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 691 (or 680 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 27.

The square root of 21428640 is about 4629.1079054176. The cubic root of 21428640 is about 277.7569084173.

The spelling of 21428640 in words is "twenty-one million, four hundred twenty-eight thousand, six hundred forty".