21688497 has 6 divisors (see below), whose sum is σ = 31327842. Its totient is φ = 14458992.

The previous prime is 21688483. The next prime is 21688523. The reversal of 21688497 is 79488612.

It can be written as a sum of positive squares in only one way, i.e., 19501056 + 2187441 = 4416^2 + 1479^2 .

It is not a de Polignac number, because 21688497 - 2¹⁰ = 21687473 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21688427) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1204908 + ... + 1204925.

It is an arithmetic number, because the mean of its divisors is an integer number (5221307).

Almost surely, 2^21688497 is an apocalyptic number.

It is an amenable number.

21688497 is a deficient number, since it is larger than the sum of its proper divisors (9639345).

21688497 is a wasteful number, since it uses less digits than its factorization.

21688497 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2409839 (or 2409836 counting only the distinct ones).

The product of its digits is 193536, while the sum is 45.

The square root of 21688497 is about 4657.0910448476. The cubic root of 21688497 is about 278.8751512933.

The spelling of 21688497 in words is "twenty-one million, six hundred eighty-eight thousand, four hundred ninety-seven".