21663723 has 16 divisors (see below), whose sum is σ = 30640896. Its totient is φ = 13585440.

The previous prime is 21663721. The next prime is 21663751. The reversal of 21663723 is 32736612.

It is not a de Polignac number, because 21663723 - 2¹ = 21663721 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21663721) 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, 1636 + ... + 6782.

It is an arithmetic number, because the mean of its divisors is an integer number (1915056).

Almost surely, 2^21663723 is an apocalyptic number.

21663723 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21663723 is a deficient number, since it is larger than the sum of its proper divisors (8977173).

21663723 is a wasteful number, since it uses less digits than its factorization.

21663723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5234.

The product of its digits is 9072, while the sum is 30.

The square root of 21663723 is about 4654.4304699931. The cubic root of 21663723 is about 278.7689277769.

The spelling of 21663723 in words is "twenty-one million, six hundred sixty-three thousand, seven hundred twenty-three".