21285820 has 24 divisors (see below), whose sum is σ = 44974944. Its totient is φ = 8462016.

The previous prime is 21285811. The next prime is 21285821. The reversal of 21285820 is 2858212.

It is a super-2 number, since 2×21285820² = 906172266144800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21285821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 154 + ... + 6526.

It is an arithmetic number, because the mean of its divisors is an integer number (1873956).

Almost surely, 2^21285820 is an apocalyptic number.

21285820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21285820 is an abundant number, since it is smaller than the sum of its proper divisors (23689124).

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

21285820 is a wasteful number, since it uses less digits than its factorization.

21285820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6549 (or 6547 counting only the distinct ones).

The product of its (nonzero) digits is 2560, while the sum is 28.

The square root of 21285820 is about 4613.6558172451. The cubic root of 21285820 is about 277.1384572835.

It can be divided in two parts, 212858 and 20, that added together give a triangular number (212878 = T₆₅₂).

The spelling of 21285820 in words is "twenty-one million, two hundred eighty-five thousand, eight hundred twenty".