21284840 has 64 divisors (see below), whose sum is σ = 50544000. Its totient is φ = 8055040.

The previous prime is 21284839. The next prime is 21284903. The reversal of 21284840 is 4848212.

It is a Harshad number since it is a multiple of its sum of digits (29).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 68285 + ... + 68595.

It is an arithmetic number, because the mean of its divisors is an integer number (789750).

Almost surely, 2^21284840 is an apocalyptic number.

21284840 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 21284840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25272000).

21284840 is an abundant number, since it is smaller than the sum of its proper divisors (29259160).

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

21284840 is a wasteful number, since it uses less digits than its factorization.

21284840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 410 (or 406 counting only the distinct ones).

The product of its (nonzero) digits is 4096, while the sum is 29.

The square root of 21284840 is about 4613.5496095740. The cubic root of 21284840 is about 277.1342040631.

The spelling of 21284840 in words is "twenty-one million, two hundred eighty-four thousand, eight hundred forty".