21090723 has 8 divisors (see below), whose sum is σ = 28148736. Its totient is φ = 14046600.

The previous prime is 21090721. The next prime is 21090731. The reversal of 21090723 is 32709012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21090723 - 2¹ = 21090721 is a prime.

It is a Smith number, since the sum of its digits (24) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

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

It is a junction number, because it is equal to n+sod(n) for n = 21090693 and 21090702.

It is not an unprimeable number, because it can be changed into a prime (21090721) 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 7 ways as a sum of consecutive naturals, for example, 838 + ... + 6548.

It is an arithmetic number, because the mean of its divisors is an integer number (3518592).

Almost surely, 2^21090723 is an apocalyptic number.

21090723 is a deficient number, since it is larger than the sum of its proper divisors (7058013).

21090723 is a wasteful number, since it uses less digits than its factorization.

21090723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6945.

The product of its (nonzero) digits is 756, while the sum is 24.

The square root of 21090723 is about 4592.4637178752. The cubic root of 21090723 is about 276.2891450981.

Adding to 21090723 its reverse (32709012), we get a palindrome (53799735).

The spelling of 21090723 in words is "twenty-one million, ninety thousand, seven hundred twenty-three".