21390423 has 4 divisors (see below), whose sum is σ = 28520568. Its totient is φ = 14260280.

The previous prime is 21390389. The next prime is 21390427. The reversal of 21390423 is 32409312.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21390423 - 2¹⁸ = 21128279 is a prime.

It is a super-2 number, since 2×21390423² = 915100392237858, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21390393 and 21390402.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390427) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3565068 + ... + 3565073.

It is an arithmetic number, because the mean of its divisors is an integer number (7130142).

Almost surely, 2^21390423 is an apocalyptic number.

21390423 is a deficient number, since it is larger than the sum of its proper divisors (7130145).

21390423 is an equidigital number, since it uses as much as digits as its factorization.

21390423 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7130144.

The product of its (nonzero) digits is 1296, while the sum is 24.

The square root of 21390423 is about 4624.9781621106. The cubic root of 21390423 is about 277.5916879070.

Adding to 21390423 its reverse (32409312), we get a palindrome (53799735).

The spelling of 21390423 in words is "twenty-one million, three hundred ninety thousand, four hundred twenty-three".