21688557 has 16 divisors (see below), whose sum is σ = 33208320. Its totient is φ = 12452400.

The previous prime is 21688547. The next prime is 21688559. The reversal of 21688557 is 75588612.

It is not a de Polignac number, because 21688557 - 2⁸ = 21688301 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21688559) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16669 + ... + 17922.

It is an arithmetic number, because the mean of its divisors is an integer number (2075520).

Almost surely, 2^21688557 is an apocalyptic number.

It is an amenable number.

21688557 is a deficient number, since it is larger than the sum of its proper divisors (11519763).

21688557 is a wasteful number, since it uses less digits than its factorization.

21688557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34624.

The product of its digits is 134400, while the sum is 42.

The square root of 21688557 is about 4657.0974866326. The cubic root of 21688557 is about 278.8754084572.

The spelling of 21688557 in words is "twenty-one million, six hundred eighty-eight thousand, five hundred fifty-seven".