21390723 has 10 divisors (see below), whose sum is σ = 31954164. Its totient is φ = 14260428.

The previous prime is 21390673. The next prime is 21390727. The reversal of 21390723 is 32709312.

It is not a de Polignac number, because 21390723 - 2⁶ = 21390659 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21390727) 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 9 ways as a sum of consecutive naturals, for example, 131961 + ... + 132122.

Almost surely, 2^21390723 is an apocalyptic number.

21390723 is a deficient number, since it is larger than the sum of its proper divisors (10563441).

21390723 is an equidigital number, since it uses as much as digits as its factorization.

21390723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 264095 (or 264086 counting only the distinct ones).

The product of its (nonzero) digits is 2268, while the sum is 27.

The square root of 21390723 is about 4625.0105945825. The cubic root of 21390723 is about 277.5929856392.

The spelling of 21390723 in words is "twenty-one million, three hundred ninety thousand, seven hundred twenty-three".