21687124 has 12 divisors (see below), whose sum is σ = 38328948. Its totient is φ = 10736000.

The previous prime is 21687119. The next prime is 21687191. The reversal of 21687124 is 42178612.

It can be written as a sum of positive squares in 2 ways, for example, as 15840400 + 5846724 = 3980^2 + 2418^2 .

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 26437 + ... + 27244.

It is an arithmetic number, because the mean of its divisors is an integer number (3194079).

Almost surely, 2^21687124 is an apocalyptic number.

It is an amenable number.

21687124 is a deficient number, since it is larger than the sum of its proper divisors (16641824).

21687124 is a wasteful number, since it uses less digits than its factorization.

21687124 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53786 (or 53784 counting only the distinct ones).

The product of its digits is 5376, while the sum is 31.

The square root of 21687124 is about 4656.9436328992. The cubic root of 21687124 is about 278.8692663970.

The spelling of 21687124 in words is "twenty-one million, six hundred eighty-seven thousand, one hundred twenty-four".