21665523 has 16 divisors (see below), whose sum is σ = 32601600. Its totient is φ = 12677280.

The previous prime is 21665521. The next prime is 21665551. The reversal of 21665523 is 32556612.

It is not a de Polignac number, because 21665523 - 2¹ = 21665521 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21665521) 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, 10363 + ... + 12276.

It is an arithmetic number, because the mean of its divisors is an integer number (2037600).

Almost surely, 2^21665523 is an apocalyptic number.

21665523 is a deficient number, since it is larger than the sum of its proper divisors (10936077).

21665523 is a wasteful number, since it uses less digits than its factorization.

21665523 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22682.

The product of its digits is 10800, while the sum is 30.

The square root of 21665523 is about 4654.6238301285. The cubic root of 21665523 is about 278.7766483670.

The spelling of 21665523 in words is "twenty-one million, six hundred sixty-five thousand, five hundred twenty-three".