21021684 has 24 divisors (see below), whose sum is σ = 50248128. Its totient is φ = 6836160.

The previous prime is 21021683. The next prime is 21021697. The reversal of 21021684 is 48612012.

It is a super-2 number, since 2×21021684² = 883822396391712, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021683) 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, 20872 + ... + 21855.

It is an arithmetic number, because the mean of its divisors is an integer number (2093672).

Almost surely, 2^21021684 is an apocalyptic number.

It is an amenable number.

21021684 is an abundant number, since it is smaller than the sum of its proper divisors (29226444).

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

21021684 is a wasteful number, since it uses less digits than its factorization.

21021684 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42775 (or 42773 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 24.

The square root of 21021684 is about 4584.9410028920. The cubic root of 21021684 is about 275.9873445153.

Adding to 21021684 its reverse (48612012), we get a palindrome (69633696).

The spelling of 21021684 in words is "twenty-one million, twenty-one thousand, six hundred eighty-four".