21660023 has 16 divisors (see below), whose sum is σ = 28594944. Its totient is φ = 15884160.

The previous prime is 21660011. The next prime is 21660047. The reversal of 21660023 is 32006612.

It is a cyclic number.

It is not a de Polignac number, because 21660023 - 2⁴ = 21660007 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21659977 and 21660004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660053) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6965 + ... + 9582.

It is an arithmetic number, because the mean of its divisors is an integer number (1787184).

Almost surely, 2^21660023 is an apocalyptic number.

21660023 is a deficient number, since it is larger than the sum of its proper divisors (6934921).

21660023 is a wasteful number, since it uses less digits than its factorization.

21660023 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16582.

The product of its (nonzero) digits is 432, while the sum is 20.

The square root of 21660023 is about 4654.0329822639. The cubic root of 21660023 is about 278.7530563320.

Adding to 21660023 its reverse (32006612), we get a palindrome (53666635).

The spelling of 21660023 in words is "twenty-one million, six hundred sixty thousand, twenty-three".