21664061 has 4 divisors (see below), whose sum is σ = 21750624. Its totient is φ = 21577500.

The previous prime is 21664051. The next prime is 21664063. The reversal of 21664061 is 16046612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21664061 - 2⁶ = 21663997 is a prime.

It is a super-4 number, since 4×21664061⁴ (a number of 30 digits) contains 4444 as substring.

It is a Duffinian number.

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 21664061.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664063) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 42905 + ... + 43406.

It is an arithmetic number, because the mean of its divisors is an integer number (5437656).

Almost surely, 2^21664061 is an apocalyptic number.

It is an amenable number.

21664061 is a deficient number, since it is larger than the sum of its proper divisors (86563).

21664061 is an equidigital number, since it uses as much as digits as its factorization.

21664061 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86562.

The product of its (nonzero) digits is 1728, while the sum is 26.

The square root of 21664061 is about 4654.4667793422. The cubic root of 21664061 is about 278.7703775648.

The spelling of 21664061 in words is "twenty-one million, six hundred sixty-four thousand, sixty-one".