21084820 has 24 divisors (see below), whose sum is σ = 45476424. Its totient is φ = 8205696.

The previous prime is 21084803. The next prime is 21084829. The reversal of 21084820 is 2848012.

It can be written as a sum of positive squares in 4 ways, for example, as 6061444 + 15023376 = 2462^2 + 3876^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21084829) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 13507 + ... + 14986.

It is an arithmetic number, because the mean of its divisors is an integer number (1894851).

Almost surely, 2^21084820 is an apocalyptic number.

21084820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21084820 is an abundant number, since it is smaller than the sum of its proper divisors (24391604).

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

21084820 is a wasteful number, since it uses less digits than its factorization.

21084820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28539 (or 28537 counting only the distinct ones).

The product of its (nonzero) digits is 1024, while the sum is 25.

The square root of 21084820 is about 4591.8209895422. The cubic root of 21084820 is about 276.2633661967.

It can be divided in two parts, 21084 and 820, that added together give a square (21904 = 148²).

The spelling of 21084820 in words is "twenty-one million, eighty-four thousand, eight hundred twenty".