21664634 has 4 divisors (see below), whose sum is σ = 32496954. Its totient is φ = 10832316.

The previous prime is 21664609. The next prime is 21664637. The reversal of 21664634 is 43646612.

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., 16024009 + 5640625 = 4003^2 + 2375^2 .

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21664634.

It is not an unprimeable number, because it can be changed into a prime (21664637) 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 as a sum of consecutive naturals, namely, 5416157 + ... + 5416160.

Almost surely, 2^21664634 is an apocalyptic number.

21664634 is a deficient number, since it is larger than the sum of its proper divisors (10832320).

21664634 is a wasteful number, since it uses less digits than its factorization.

21664634 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10832319.

The product of its digits is 20736, while the sum is 32.

The square root of 21664634 is about 4654.5283327100. The cubic root of 21664634 is about 278.7728353068.

The spelling of 21664634 in words is "twenty-one million, six hundred sixty-four thousand, six hundred thirty-four".