21678723 has 36 divisors (see below), whose sum is σ = 36474984. Its totient is φ = 12355200.

The previous prime is 21678697. The next prime is 21678731. The reversal of 21678723 is 32787612.

It is not a de Polignac number, because 21678723 - 2⁶ = 21678659 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21678733) 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 35 ways as a sum of consecutive naturals, for example, 17928 + ... + 19098.

It is an arithmetic number, because the mean of its divisors is an integer number (1013194).

Almost surely, 2^21678723 is an apocalyptic number.

21678723 is a deficient number, since it is larger than the sum of its proper divisors (14796261).

21678723 is a wasteful number, since it uses less digits than its factorization.

21678723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1216 (or 1202 counting only the distinct ones).

The product of its digits is 28224, while the sum is 36.

The square root of 21678723 is about 4656.0415590929. The cubic root of 21678723 is about 278.8332529653.

Subtracting 21678723 from its reverse (32787612), we obtain a square (11108889 = 3333²).

The spelling of 21678723 in words is "twenty-one million, six hundred seventy-eight thousand, seven hundred twenty-three".