21688437 has 16 divisors (see below), whose sum is σ = 30159360. Its totient is φ = 13848000.

The previous prime is 21688427. The next prime is 21688439. The reversal of 21688437 is 73488612.

It is not a de Polignac number, because 21688437 - 2⁴ = 21688421 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21688395 and 21688404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21688439) 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 15 ways as a sum of consecutive naturals, for example, 8239 + ... + 10547.

It is an arithmetic number, because the mean of its divisors is an integer number (1884960).

Almost surely, 2^21688437 is an apocalyptic number.

It is an amenable number.

21688437 is a deficient number, since it is larger than the sum of its proper divisors (8470923).

21688437 is a wasteful number, since it uses less digits than its factorization.

21688437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2444.

The product of its digits is 64512, while the sum is 39.

The square root of 21688437 is about 4657.0846030537. The cubic root of 21688437 is about 278.8748941289.

The spelling of 21688437 in words is "twenty-one million, six hundred eighty-eight thousand, four hundred thirty-seven".