21681360 has 60 divisors (see below), whose sum is σ = 72815652. Its totient is φ = 5781504.

The previous prime is 21681347. The next prime is 21681377. The reversal of 21681360 is 6318612.

It can be written as a sum of positive squares in 2 ways, for example, as 14837904 + 6843456 = 3852^2 + 2616^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

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 11 ways as a sum of consecutive naturals, for example, 14337 + ... + 15776.

Almost surely, 2^21681360 is an apocalyptic number.

21681360 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21681360 is an abundant number, since it is smaller than the sum of its proper divisors (51134292).

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

21681360 is a wasteful number, since it uses less digits than its factorization.

21681360 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30132 (or 30123 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21681360 is about 4656.3247309439. The cubic root of 21681360 is about 278.8445582664.

Adding to 21681360 its reverse (6318612), we get a palindrome (27999972).

The spelling of 21681360 in words is "twenty-one million, six hundred eighty-one thousand, three hundred sixty".