21688456 has 8 divisors (see below), whose sum is σ = 40665870. Its totient is φ = 10844224.

The previous prime is 21688453. The next prime is 21688477. The reversal of 21688456 is 65488612.

It can be written as a sum of positive squares in only one way, i.e., 16240900 + 5447556 = 4030^2 + 2334^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is not an unprimeable number, because it can be changed into a prime (21688453) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1355521 + ... + 1355536.

Almost surely, 2^21688456 is an apocalyptic number.

It is an amenable number.

21688456 is a deficient number, since it is larger than the sum of its proper divisors (18977414).

21688456 is a wasteful number, since it uses less digits than its factorization.

21688456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2711063 (or 2711059 counting only the distinct ones).

The product of its digits is 92160, while the sum is 40.

The square root of 21688456 is about 4657.0866429561. The cubic root of 21688456 is about 278.8749755644.

The spelling of 21688456 in words is "twenty-one million, six hundred eighty-eight thousand, four hundred fifty-six".