21306423 has 8 divisors (see below), whose sum is σ = 30079728. Its totient is φ = 13368704.

The previous prime is 21306407. The next prime is 21306431. The reversal of 21306423 is 32460312.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21306423 - 2⁴ = 21306407 is a prime.

It is a super-2 number, since 2×21306423² = 907927322109858, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21306423.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21306433) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 208836 + ... + 208937.

It is an arithmetic number, because the mean of its divisors is an integer number (3759966).

Almost surely, 2^21306423 is an apocalyptic number.

21306423 is a deficient number, since it is larger than the sum of its proper divisors (8773305).

21306423 is a wasteful number, since it uses less digits than its factorization.

21306423 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 417793.

The product of its (nonzero) digits is 864, while the sum is 21.

The square root of 21306423 is about 4615.8881052296. Note that the first 3 decimals coincide. The cubic root of 21306423 is about 277.2278445280.

Adding to 21306423 its reverse (32460312), we get a palindrome (53766735).

The spelling of 21306423 in words is "twenty-one million, three hundred six thousand, four hundred twenty-three".