21664858 has 4 divisors (see below), whose sum is σ = 32497290. Its totient is φ = 10832428.

The previous prime is 21664849. The next prime is 21664861. The reversal of 21664858 is 85846612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 21003889 + 660969 = 4583^2 + 813^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21664858.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5416213 + ... + 5416216.

Almost surely, 2^21664858 is an apocalyptic number.

21664858 is a deficient number, since it is larger than the sum of its proper divisors (10832432).

21664858 is a wasteful number, since it uses less digits than its factorization.

21664858 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10832431.

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

The square root of 21664858 is about 4654.5523952363. The cubic root of 21664858 is about 278.7737960877.

It can be divided in two parts, 21664 and 858, that added together give a palindrome (22522).

The spelling of 21664858 in words is "twenty-one million, six hundred sixty-four thousand, eight hundred fifty-eight".