21664451 has 4 divisors (see below), whose sum is σ = 21810000. Its totient is φ = 21518904.

The previous prime is 21664417. The next prime is 21664457. The reversal of 21664451 is 15446612.

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

It is a cyclic number.

It is not a de Polignac number, because 21664451 - 2¹⁰ = 21663427 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21664457) by changing a digit.

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 in 3 ways as a sum of consecutive naturals, for example, 72551 + ... + 72848.

It is an arithmetic number, because the mean of its divisors is an integer number (5452500).

Almost surely, 2^21664451 is an apocalyptic number.

21664451 is a deficient number, since it is larger than the sum of its proper divisors (145549).

21664451 is a wasteful number, since it uses less digits than its factorization.

21664451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 145548.

The product of its digits is 5760, while the sum is 29.

The square root of 21664451 is about 4654.5086743930. The cubic root of 21664451 is about 278.7720503782.

The spelling of 21664451 in words is "twenty-one million, six hundred sixty-four thousand, four hundred fifty-one".