21285840 has 80 divisors (see below), whose sum is σ = 68138496. Its totient is φ = 5491200.

The previous prime is 21285821. The next prime is 21285857. The reversal of 21285840 is 4858212.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21285798 and 21285807.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6010 + ... + 8870.

Almost surely, 2^21285840 is an apocalyptic number.

21285840 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 21285840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34069248).

21285840 is an abundant number, since it is smaller than the sum of its proper divisors (46852656).

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

21285840 is a wasteful number, since it uses less digits than its factorization.

21285840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2908 (or 2902 counting only the distinct ones).

The product of its (nonzero) digits is 5120, while the sum is 30.

The square root of 21285840 is about 4613.6579847232. The cubic root of 21285840 is about 277.1385440826.

The spelling of 21285840 in words is "twenty-one million, two hundred eighty-five thousand, eight hundred forty".